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8/2(2+2) what do you come up with? (Original Post) kimbutgar Aug 2019 OP
16. nt Atticus Aug 2019 #1
+1 indeed 16 is the correct answer nt mr_lebowski Aug 2019 #2
uh huh.. Maxheader Aug 2019 #155
Not following you ... I said 16 is the correct answer ... mr_lebowski Aug 2019 #158
It was my understanding that there would be no math TeamPooka Aug 2019 #92
hahahaha. n/t OneGrassRoot Aug 2019 #120
You win the internet today KentuckyWoman Aug 2019 #131
I was right the other day my SO brought this up from FB... Anon-C Aug 2019 #3
Nothing, 16 is absolutely the correct answer ... someone else is missing something ;) mr_lebowski Aug 2019 #4
16 Dr. Strange Aug 2019 #5
Ok I'm a substitute teacher who is learning common core kimbutgar Aug 2019 #6
That is silly. Drahthaardogs Aug 2019 #8
4x1/4 is 1 kimbutgar Aug 2019 #20
Correct, but it is not the same problem. n/t Ms. Toad Aug 2019 #23
Yeah. But that has nothing to do with the equation in question. GulfCoast66 Aug 2019 #34
wut? jcgoldie Aug 2019 #10
I would appreciate a link to an explanation of that method missingthebigdog Aug 2019 #24
Seconded! FiveGoodMen Aug 2019 #98
As someone with two math degrees - Ms. Toad Aug 2019 #37
If that is what they are teaching children those children are going to be seriously math challenged. honest.abe Aug 2019 #60
It is 8 divided by 2, not 2 divided by 8 LeftInTX Aug 2019 #152
Please Excuse My Dear Aunt Sally jcgoldie Aug 2019 #7
That's right! customerserviceguy Aug 2019 #28
1 SlogginThroughIt Aug 2019 #9
Pemdas SlogginThroughIt Aug 2019 #11
No jcgoldie Aug 2019 #12
oh really? SlogginThroughIt Aug 2019 #15
I promise jcgoldie Aug 2019 #18
Yeah, same with addition and subtraction. Dr. Strange Aug 2019 #30
Yup. (Former math teacher) Ms. Toad Aug 2019 #22
Perhaps more accurately (PE(MD)(AS)) mr_lebowski Aug 2019 #35
A hole in your argument. KY_EnviroGuy Aug 2019 #137
Exactly. tinrobot Aug 2019 #16
You only do 4 passes, not 6 Ms. Toad Aug 2019 #19
That was a great explanation! jcgoldie Aug 2019 #26
Shaking 30 year old cobwebs out of my math teaching brain . . . Ms. Toad Aug 2019 #39
I came up with 16. Polly Hennessey Aug 2019 #13
No one who knows anything about calculations would write a formula like that because they'd Hoyt Aug 2019 #14
My point exactly wryter2000 Aug 2019 #80
Yup... SidDithers Aug 2019 #86
In the old days we used Reverse Polish Notation and we liked it. hunter Aug 2019 #133
My initial solution was 16 based on what I know it's 16 kimbutgar Aug 2019 #17
I mastered the equation from an former Nazi rocket fuel scientist while I was in the Army Brother Buzz Aug 2019 #25
Here is how you get to 1: missingthebigdog Aug 2019 #21
1 applegrove Aug 2019 #27
1 Turbineguy Aug 2019 #29
This was covered in the above discussion jcgoldie Aug 2019 #33
Goodness. I learned this in 8th grade! GulfCoast66 Aug 2019 #31
1. Nt BootinUp Aug 2019 #32
It's actually 16 my good friend ... mr_lebowski Aug 2019 #36
Weed relaxed error, that's my story, lol. BootinUp Aug 2019 #42
I get stoned as I pray ... check this one out brother ... from last year ... mr_lebowski Aug 2019 #44
You got good taste in music jcgoldie Aug 2019 #91
I like fishwax's answer, #45 best. hunter Aug 2019 #48
Fake math. The answer is what i say it is. dem4decades Aug 2019 #38
Ah yes! Mossfern Aug 2019 #84
Well, you're the president Clash City Rocker Aug 2019 #101
My high school algebra teacher got fired the year after I was in her class. 3catwoman3 Aug 2019 #40
6.693 x 10 to the power 25 sarisataka Aug 2019 #41
I come up with .... rufus dog Aug 2019 #43
fraction bars function the same as brackets/parens, which is how people are getting the answer 1 fishwax Aug 2019 #45
It occurred to me that people are taking the / to refer to a fraction bar jcgoldie Aug 2019 #49
You're right about the keyboard, but the same principle applies w/ an elementary division symbol fishwax Aug 2019 #68
Arbitrary jcgoldie Aug 2019 #75
I agree with you, though do appreciate the exposition by fishwax mr_lebowski Aug 2019 #82
Yes I agree jcgoldie Aug 2019 #89
yeah, looking back I wound up being more confusing than I intended with my initial post fishwax Aug 2019 #122
but it is arbitrary, as your own final few sentences show fishwax Aug 2019 #93
Just to cherry pick one sentence... jcgoldie Aug 2019 #97
that's cool about the calculators fishwax Aug 2019 #100
No; putting it into my scientific calculator, using in place of / muriel_volestrangler Aug 2019 #134
That's exactly what I did to get 1. The bar is a division bar, and Nay Aug 2019 #153
The good old fraction bar! LeftInTX Aug 2019 #150
Shunting-yard algorithm? hunter Aug 2019 #46
A big yawn! struggle4progress Aug 2019 #47
1 treestar Aug 2019 #50
Did'nt we haves this test a few weeks back? Hotler Aug 2019 #51
166.6666% Incorrect blugbox Aug 2019 #64
8/2(2+2) 8/2(4) 8/8 1 Afromania Aug 2019 #52
multiplication and division have the same precedence so go left to right... Joe941 Aug 2019 #102
It's newer notation LeftInTX Aug 2019 #159
88 FBaggins Aug 2019 #53
Lounge??? Nt USALiberal Aug 2019 #54
Typed into MS Excel Trumpocalypse Aug 2019 #55
People rember PEMDAS, but forget the rest of the rules of operation. Hotler Aug 2019 #56
Calm down everybody kimbutgar Aug 2019 #57
Its a math problem jcgoldie Aug 2019 #66
8/2 means 8 divided by 2. Ms. Toad Aug 2019 #72
It's 16. Getting to 1 is possible but not accurate. Claritie Pixie Aug 2019 #58
An equation should never be written that way. honest.abe Aug 2019 #59
we should ALL demand non-ambiguous math!!! not_the_one Aug 2019 #69
(8/2) is redundant. Ms. Toad Aug 2019 #70
A necessary minor redundancy to eliminate confusion like we see in this thread. honest.abe Aug 2019 #73
I'm a programmer, as well, Ms. Toad Aug 2019 #104
I suppose you could get away with it.. honest.abe Aug 2019 #105
Any programmer Ms. Toad Aug 2019 #106
Well we certainly see things differently. honest.abe Aug 2019 #110
We do. Ms. Toad Aug 2019 #112
So those confused by this arbitrary math rule have less than 7th grade math skills?? honest.abe Aug 2019 #113
You seem to be confusing the level at which math skills are taught Ms. Toad Aug 2019 #116
FWIW, if you enter the equation into Google search it formats the equation exactly I wrote it. honest.abe Aug 2019 #123
It's still redundant, Ms. Toad Aug 2019 #124
I think the Google search engineers and I are more correct. honest.abe Aug 2019 #125
I had a degree in math from 1978 and I wrote programs as part of that degree LeftInTX Aug 2019 #162
Considerably different computing power in those days. Ms. Toad Aug 2019 #163
It's a grotesque thing. hunter Aug 2019 #108
True. n/t Ms. Toad Aug 2019 #109
Exactly. The point of writing equations (or anything) is to make the meaning clear to the reader. DanTex Aug 2019 #94
1 Proud Liberal Dem Aug 2019 #61
... jcgoldie Aug 2019 #63
16. jmg257 Aug 2019 #62
One FakeNoose Aug 2019 #65
I hope the original problem looked more like this: Rstrstx Aug 2019 #67
1 nini Aug 2019 #71
You Tube explains it: both are, or were, correct jimmy the one Aug 2019 #74
The Distributive Property gives me 1 LeftInTX Aug 2019 #156
This is boring. There are rules of sequence which are arbitrary. Who cares if you don't know it? Cicada Aug 2019 #76
A billion C_U_L8R Aug 2019 #77
Don't be fragile Midnightwalk Aug 2019 #78
How it's written is misleading wryter2000 Aug 2019 #79
White and gold. If you think it's blue and black, you're wrong. JustABozoOnThisBus Aug 2019 #81
My guess was 1 Tommy_Carcetti Aug 2019 #83
If it's ambiguous, then it's not a good mathematical question... SidDithers Aug 2019 #85
Eight halves is 4 Mossfern Aug 2019 #87
Ah shit pwb Aug 2019 #88
42. Douglas Adams said it, I believe it, and that settles it. Buns_of_Fire Aug 2019 #90
Parentheses first which is 4 ismnotwasm Aug 2019 #95
A poorly written mathematical expression. DanTex Aug 2019 #96
Reminds me of this classical Chinese poem 2020Junker Aug 2019 #99
yeah the problem with this is... Takket Aug 2019 #103
It's an ambiguous question, and depends on leftmost or rightmost binding rules Recursion Aug 2019 #107
Mr Cash would be proud. lpbk2713 Aug 2019 #111
PEMDAS tells me it's 16. DangerousRhythm Aug 2019 #114
Technically it could be either as multiplication and division are equal. NutmegYankee Aug 2019 #129
1 mfcorey1 Aug 2019 #115
Potatoe. LuckyCharms Aug 2019 #117
Tomatoe MadLinguist Aug 2019 #127
1 GeorgeGist Aug 2019 #118
This Is an exercise in ambiguity Silver Swan Aug 2019 #119
At least it got us off politics ! kimbutgar Aug 2019 #121
16 wendyb-NC Aug 2019 #126
8 divided by 2 multiplied by 4 equals 16 aikoaiko Aug 2019 #128
In the 50's they taught me 16 KentuckyWoman Aug 2019 #130
16 denbot Aug 2019 #132
What is the following: muriel_volestrangler Aug 2019 #135
20,000. KY_EnviroGuy Aug 2019 #138
One KY_EnviroGuy Aug 2019 #136
No that would be Trumpocalypse Aug 2019 #139
A counter-example to your interpretation comes from the Feynman lectures muriel_volestrangler Aug 2019 #140
Type it into excel Trumpocalypse Aug 2019 #141
Hmm, what do I consider more authoritative, Richard Feynman, or Excel? muriel_volestrangler Aug 2019 #142
Excel. Trumpocalypse Aug 2019 #143
Nobel. muriel_volestrangler Aug 2019 #145
No Excel it the standard Trumpocalypse Aug 2019 #147
As punchlines go, that's an unexpected one, but pretty funny (nt) muriel_volestrangler Aug 2019 #148
Except writing it with a fraction bar as you did... jcgoldie Aug 2019 #144
No, implicit multiplication is conventional muriel_volestrangler Aug 2019 #146
You hit the nail on the head. Conventions have changed..... KY_EnviroGuy Aug 2019 #149
So in modern math what is LeftInTX Aug 2019 #161
Interesting. honest.abe Aug 2019 #164
1 5X Aug 2019 #151
1 Throck Aug 2019 #154
I shall go for a beer. Throck Aug 2019 #160
Poorly written equation zipplewrath Aug 2019 #157

Maxheader

(4,373 posts)
155. uh huh..
Sat Aug 10, 2019, 01:20 PM
Aug 2019

Watch me show how to put a stick in it..

Preform the operation in parens..= 4...
Multply numerator and denomerator
4 times 8 = 32
divided by 2 = 16
 

mr_lebowski

(33,643 posts)
158. Not following you ... I said 16 is the correct answer ...
Sat Aug 10, 2019, 01:36 PM
Aug 2019

How are you putting a stick in it?

Also ... Booooooo Chiefs!

Anon-C

(3,430 posts)
3. I was right the other day my SO brought this up from FB...
Wed Aug 7, 2019, 11:23 PM
Aug 2019

...Google seems to agree with me. What am I missing?

 

mr_lebowski

(33,643 posts)
4. Nothing, 16 is absolutely the correct answer ... someone else is missing something ;)
Wed Aug 7, 2019, 11:26 PM
Aug 2019

The other possible answer is 1, but that's wrong ... operations happen left to right, beginning with multiplication/division, then addition/subtraction. Although parentheses override that.

So 8/(2(2+2)) would be 1. But not 8/2(2+2).

kimbutgar

(21,155 posts)
6. Ok I'm a substitute teacher who is learning common core
Wed Aug 7, 2019, 11:29 PM
Aug 2019

This is how they come up with 1.

8/2 = 8 as a decimal of 2 hence 1/16
1/16x2 = 1/8
1/8 x 2 = 1/4
1/4 (4 ) = 1

I lost my mind as a 63 year old that I had learned this new math

jcgoldie

(11,631 posts)
10. wut?
Wed Aug 7, 2019, 11:35 PM
Aug 2019

Division and multiplication left to right after you add inside parenthesis... its 16.

The way you would get 1 is by writing it like this... 8/(2(2+2)) placing the multiplication in the denominator.

missingthebigdog

(1,233 posts)
24. I would appreciate a link to an explanation of that method
Wed Aug 7, 2019, 11:56 PM
Aug 2019

In no universe does 8/2=1/16. “8 as a decimal of 2” makes no sense to me....

Ms. Toad

(34,074 posts)
37. As someone with two math degrees -
Thu Aug 8, 2019, 12:18 AM
Aug 2019

Your first line makes no sense.

I also generally think that common core - like the "new math" you likely learned as a child - is mathematically sound. Unfortunately, like new math, it is largely taught by people who don't understand the logical basis for it. That makes it a frustrating, meaningless exercise. I didn't understand the power of "new math" until I was working on my Master's degree in applied math, because it was taught as rote exercises, completely disconnected from its mathematical power.

Common core doesn't have the mathematical power of "new math," but it is draws on things people of our age did because they made math without calculators easier. Some of the crazy addition and subtraction rely on the same principles we used to use to count out change by counting up to the nearest coin, then to the nearest bill.

That said - I don't have a clue what you mean by your first line.

honest.abe

(8,678 posts)
60. If that is what they are teaching children those children are going to be seriously math challenged.
Thu Aug 8, 2019, 12:37 PM
Aug 2019

What you wrote is complete non-sense from a mathematical point of view.

LeftInTX

(25,364 posts)
152. It is 8 divided by 2, not 2 divided by 8
Sat Aug 10, 2019, 12:53 PM
Aug 2019


Without locating fancy keys, I can't find the appropriate math symbols.
 

SlogginThroughIt

(1,977 posts)
11. Pemdas
Wed Aug 7, 2019, 11:40 PM
Aug 2019

Parentheses
Exponents
Multiplication
Division
Addition
Subtraction

First you have to do what is in the parentheses 2+2 = 4
We have no exponents
Next we have to do the multiplication 2x4= 8
Now we do the division which is 8/8=1

jcgoldie

(11,631 posts)
12. No
Wed Aug 7, 2019, 11:41 PM
Aug 2019

Multiplication is not a higher operation than division. It is done from left to right, the acronym doesn't really capture that point.

jcgoldie

(11,631 posts)
18. I promise
Wed Aug 7, 2019, 11:49 PM
Aug 2019

And I teach HS math... just drop that little formula in any scientific calculator which I assure you is programmed to compute with the correct order of operations and it will tell you the same.

Dr. Strange

(25,921 posts)
30. Yeah, same with addition and subtraction.
Thu Aug 8, 2019, 12:03 AM
Aug 2019

Division is really just multiplication. So 8/2(2+2) can be viewed as
8 x (1/2) x (2 + 2)
since dividing by 2 is the same as multiplying as 1/2.

 

mr_lebowski

(33,643 posts)
35. Perhaps more accurately (PE(MD)(AS))
Thu Aug 8, 2019, 12:08 AM
Aug 2019

Multiplication and Division are equal in terms of order of operations, so whichever is first left to right is done first. Same with Addition and Subtraction.

KY_EnviroGuy

(14,492 posts)
137. A hole in your argument.
Sat Aug 10, 2019, 06:03 AM
Aug 2019

See post #136.

Using your rule, proceed to complete the denominator from left to right, then the final division.

KY......

Ms. Toad

(34,074 posts)
19. You only do 4 passes, not 6
Wed Aug 7, 2019, 11:49 PM
Aug 2019

P - E - MD - AS

As a former math teacher, I hate it that sloppy acronym, since it leads people to incorrect results.

Multiplication and division are equal priority - so you do whichever you encounter first, from left to right.
Same for addition and subtraction.

You can see this by recognizing that division is just multiplication by the reciprocol - so you have to get the same answer whether you divide by 2 or multiply by 1/2.

swapping *1/2 for /2, the problem becomes: 8 * 1/2 * (2+2)

8*1/2*4, doing the multiplicaiton from left to right = 4*4 = 16.

The fact that you get a different answer merely by changing it to a pure multiplication should tell you that you don't do all multiplication before doing division.

(Same for addition and subtraction. All subtraction is really just adding a negative, so they have to be the same priority)

Ms. Toad

(34,074 posts)
39. Shaking 30 year old cobwebs out of my math teaching brain . . .
Thu Aug 8, 2019, 12:22 AM
Aug 2019

Not much use these days since I'm now teaching law.

But I did have to explain basic rules for percentages to a colleague.

 

Hoyt

(54,770 posts)
14. No one who knows anything about calculations would write a formula like that because they'd
Wed Aug 7, 2019, 11:42 PM
Aug 2019

know too many people, or even some computer formulas, are going to get that right. That’s how things get really screwed up.

hunter

(38,316 posts)
133. In the old days we used Reverse Polish Notation and we liked it.
Sat Aug 10, 2019, 02:05 AM
Aug 2019


https://en.wikipedia.org/wiki/HP-35

The computer programming language Forth also works that way.

You had to have a pretty clear idea of what you were actually trying to do before embarking on any calculation.

With practice each little chunk of the calculation often corresponded to something tangible in the system you were exploring so you didn't have to wait for the ending, pushing that "equals" button, to know you'd gone astray.


kimbutgar

(21,155 posts)
17. My initial solution was 16 based on what I know it's 16
Wed Aug 7, 2019, 11:45 PM
Aug 2019

But I figured out why someone would say 1 the way they teach math nowadays.

Brother Buzz

(36,440 posts)
25. I mastered the equation from an former Nazi rocket fuel scientist while I was in the Army
Wed Aug 7, 2019, 11:58 PM
Aug 2019

It's a long and bizarre story how he ended up teaching me, but what I learned from him stood me well in college. I came up with 1.

missingthebigdog

(1,233 posts)
21. Here is how you get to 1:
Wed Aug 7, 2019, 11:50 PM
Aug 2019

8/2(2+2)=
8/2(4)=
8/2*4=
8/8=
1

The error is in using the PEMDAS (or Please Excuse my dear Aunt Sallly- parenthesis exponents multiplication division addition subtraction) mnemonic too stringently. If you follow the mnemonic, the multiplication comes before the division, so you resolve that equation after elimination of the parentheses.

However, multiplication and division are actually treated equally in order of operations (as are addition and subtraction), so the correct method is to solve from left to right once the parentheses are eliminated:

8/2(2+2)=
8/2(4)=
8/2*4=
4*4=
16

jcgoldie

(11,631 posts)
33. This was covered in the above discussion
Thu Aug 8, 2019, 12:04 AM
Aug 2019

Division and Multiplication have the same weight. For the best explanation please read post #19 by Ms Toad.

GulfCoast66

(11,949 posts)
31. Goodness. I learned this in 8th grade!
Thu Aug 8, 2019, 12:04 AM
Aug 2019

Do the equation left to right but parentheses are done before factoring into the rest of the equation. Hence the parentheses!

16.

I used to be able to tell you the law that drove this. Some dude from 500 years ago I’m sure! But I was a fair math student at best. Did just good enough to get a plant science degree.

Ok. Never made lower than a B but only went up to calc 2 in college. Can’t remember any of that shit!

hunter

(38,316 posts)
48. I like fishwax's answer, #45 best.
Thu Aug 8, 2019, 03:37 AM
Aug 2019
https://www.democraticunderground.com/100212359398#post45

Anyone writing this out by hand, or as a computer program, wouldn't write it this way.

The purpose of this convention was to make life easier for typesetters.

This typesetting convention was then beaten into a dead joyless math "fact" that was force fed to middle school students.

3catwoman3

(24,005 posts)
40. My high school algebra teacher got fired the year after I was in her class.
Thu Aug 8, 2019, 12:36 AM
Aug 2019

I thought I just didn't get it. Turned out a lot of her students didn't get it.

My senior year of high school, the final quarter in math was calculus. The teacher handed us a slender black book and said, "Here. This is all self-explanatory." Like hell it was!

Some years ago, my husband gave me a book entitled Math Without Tears. I gave up by page 6 after reading it 10 times.

Nonetheless, I must have learned something. I came up with 16 -

sarisataka

(18,656 posts)
41. 6.693 x 10 to the power 25
Thu Aug 8, 2019, 12:57 AM
Aug 2019

6.693x10^25

Oh wait, I forgot to carry the 3...

It's 16, as well explained above

fishwax

(29,149 posts)
45. fraction bars function the same as brackets/parens, which is how people are getting the answer 1
Thu Aug 8, 2019, 01:31 AM
Aug 2019

The dispute here is basically one involving different mathematical grammars. It's a result of an evolution in the grammar of mathematical notation that stems from the rise of computer-programmed calculations, the fact that typesetting vertical fractions is difficult, and the fact that basic keyboards have no simple key for the traditional division symbol.

In the beginning there was a horizontal fraction bar, and it functioned as a grouping symbol. Everything above the line (the numerator) was grouped as though with an implied parenthesis and everything below the line (denominator) was grouped. But vertical fractions (with a horizontal fraction bar) are difficult to typeset, and so the diagonal fraction was introduced in the 18th century.

The fraction slash, unlike the horizontal fraction bar, is not a grouping symbol--however, traditionally typesetting for algebraic functions held that the diagonal slash grouped together everything immediately before it (that is to say, everything not separated by a space or a function symbol was the numerator) and everything immediately after it (everything connected to the slash bar and not separated by a space or an explicit function symbol was the denominator). So, for example, b/cd would group the quantity of c times d as the denominator, and therefore that would take place first in the order of operations. In my experience (as a student and then later as a typesetter and editor for educational publishers) that is the convention that textbooks and instructional manuals followed.

That convention, though, doesn't translate to computer programming, where the parenthesis becomes essential because generally (I'm not an expert here on coding, but this is my understanding) programming languages are going to require an explicit function. You can't put cd in a computer code and have the program understand that you are multiplying c times d. You have to include the operator.

The equation in the OP basically follows the pattern of a/bc, where a = 8, b = 2, and c = (2+2) = 4. The ambiguity arises because it isn't specifically clear whether a/bc is meant to be read as (a/b)c or a/(bc). It just depends on which grammar convention one uses.

My instinct (because of my background in typesetting and editorial) is to treat "bc" as the denominator of a fraction. It seems odd to me to say that a/bc = ac/b. Or that 4a/a(a+a) = 8a rather than the (to me) more intuitive 4/(a+a). But, again, that's because my training is rooted heavily in the latter. I don't know how widespread that convention is in educational textbooks today--my guess is that, with the increasing prominence of programming languages, texts would be more inclined to use parentheses to eliminate any potential ambiguity. I believe that there are some fields (for example, academic journals in physics) which still treat implicit multiplication immediately before or after a fractional slash as the numerator or denominator.

jcgoldie

(11,631 posts)
49. It occurred to me that people are taking the / to refer to a fraction bar
Thu Aug 8, 2019, 09:40 AM
Aug 2019

Thereby implicitly adding a second set of parenthesis and pushing the multiplication into the denominator. The reason I believe that is a mistake, however, in any application and not just computer programming language as you cited is that the "/" is really the only way on a standard keyboard to express division. There's no "÷" on the keyboard. Therefore its how we write division without grouping and if we want to show that everything after the / should be divided by we have to introduce parenthesis. This isn't really obscure, kids have been required to know this to correctly use any scientific or graphing calculator in HS math class for 20 years.

fishwax

(29,149 posts)
68. You're right about the keyboard, but the same principle applies w/ an elementary division symbol
Thu Aug 8, 2019, 01:06 PM
Aug 2019

The use of the "/" on keyboards (as I noted in my first paragraph before) is one of the factors that has led to this shift in conventions, but even without considering it as a fraction bar the principle of implicit multiplication (or multiplication by juxtaposition) taking precedence in the order of operations has a longstanding tradition behind it. This doesn't come up until you start introducing variables (at which point the "÷" symbol tends to be phased out).

When variables are juxtaposed, we tend to group those as a single unit: ab is equal to a times b, but we generally read it as simply "ab" ... and so if someone were to write "3 ÷ ab" this would bring a tendency to read that as 3 divided by ab (3/(ab)) rather than 3 divided by a times b. Simiilarly, when we see 2x we see that as a discrete unit (two times the value of x) rather than as two separate units (2 X x). This convention also isn't obscure, and is still used in some contexts.

Neither approach is obscure, exactly, which is why, unless one could expect everyone reading to understand the convention in play, it would be best to write 3/(ab) or (3/a)b, depending on which is intended. The fact is that, unlike, say 2+2=4, the order of operations is an entirely arbitrary convention. As such, it is subject to shifting across time and contexts.

jcgoldie

(11,631 posts)
75. Arbitrary
Thu Aug 8, 2019, 01:25 PM
Aug 2019

No I disagree. I do not know anything about "implicit multiplication" except to know that in this case it is wrong. I understand that its an assumption that people are making which you are explaining... but it is still an incorrect assumption. There is no way to prioritize multiplication without undermining the very definition of division as multiplication by reciprocals (ie 8/2 = 8*(1/2)) If you take the ACT test there's only one right answer to this simple problem. If you punch it into any scientific calculator, it will compute it in the same way. If you pick up any elementary algebra textbook which has been modernized to the point that kids use calculators or computers for basic computation... you will see it written in this way and not with the added parenthesis around 8/2... in fact it is often written in this way for just the purpose of teasing out this misunderstanding of the rule.

 

mr_lebowski

(33,643 posts)
82. I agree with you, though do appreciate the exposition by fishwax
Thu Aug 8, 2019, 01:43 PM
Aug 2019

I take issue with his/her general notion that there's any sort of implicit grouping on either side of a division sign, the talk of what 'immediately before' and 'immediately after' being understood to be 'grouped' and meant to happen earlier in the OOO. I've never heard of this and cannot imagine this was ever commonly understood to be the case. Could be wrong though

The fraction slash, unlike the horizontal fraction bar, is not a grouping symbol--however, traditionally typesetting for algebraic functions held that the diagonal slash grouped together everything immediately before it (that is to say, everything not separated by a space or a function symbol was the numerator) and everything immediately after it (everything connected to the slash bar and not separated by a space or an explicit function symbol was the denominator). So, for example, b/cd would group the quantity of c times d as the denominator, and therefore that would take place first in the order of operations.

jcgoldie

(11,631 posts)
89. Yes I agree
Thu Aug 8, 2019, 01:59 PM
Aug 2019

It was definitely a more interesting argument than I anticipated. Now I have to leave this thread that I'm sure is boring the pants off 98% of DU because I have the next 9 months to experience the frustration of teaching mathematics and less than a week to get a zillion tomatoes picked... would any math debaters happen to know if I should blanch them before or after coring them for the freezer?!?

Edit: Wife finally responded to text... "core first then blanch, too hot and mushy after"... almost got me excited...

fishwax

(29,149 posts)
122. yeah, looking back I wound up being more confusing than I intended with my initial post
Thu Aug 8, 2019, 10:09 PM
Aug 2019

I think presenting it as a grouping around the slash sign was confusing on my part, and it's all because I was focusing on the typesetting angle because (a) I was thinking there was a symmetry here between the coalescence of the conventions first around the same time as the rise of movable type and now those conventions shifting as a result of a new dominant technology with the computer; and (b) I used to be a typesetter, and specifically for calculus and physics texts, so I find it a lot more interesting than most people do. But also because (c) it was like 1:30 in the morning and I wasn't thinking clearly .

Had I been thinking more clearly, I might still have mentioned typesetting offhand, but I would have focused on the simple fact that mathematicians and physicists (maybe engineers, i don't know, depending on the field, I suppose) often tend to view juxtaposed variables as single units. They're more prone to see ab as " (a * b)" rather than simply "a * b," while programmers and programs would be more likely to see ab as "a * b." Since students are more likely to be programmers (or to deal with computer programs) then to be mathematicians or physicists, though, it makes sense that in the last few decades the latter convention has overtaken academic instruction.

Nothing wrong with that. Nothing at all. But it's probably silly to assume that folks who write, read, or follow something like the style manual for the American Institute of Physics, which says you should "never write 1/3x unless you mean 1/(3x)," or the style guide for reviewers for the American Mathematical Society (http://web.archive.org/web/20011201061315/http://www.ams.org/authors/guide-reviewers.html), which says "We linearize simple formulas, using the rule that multiplication indicated by juxtaposition is carried out before division," simply don't understand basic seventh grade math.

Anyway, this comes up every couple of years when some similarly designed expression creates this sort of controversy, and I always find it entertaining. Fun to talk math, even though it's not my dominant language

fishwax

(29,149 posts)
93. but it is arbitrary, as your own final few sentences show
Thu Aug 8, 2019, 02:29 PM
Aug 2019

As I said, these conventions have shifted over the years. That's because they're arbitrary, and the assumptions underscoring the conventions have shifted. Nothing about math has shifted--the computation itself isn't arbitrary. But how we organize and present it as a language is/has. In this case these conventions have shifted, as I noted in my original post (and as you reinforce here) because of the increasing prominence of programmed calculations, among other things. You can't really put the equation, as written, in most of the calculators or computers that kids would use for calculation, because doing so would require you to insert the operation symbol between two juxtaposed values after the slash. (Or, the program might be written to enter it automatically.) Again, that's not because this is the one and only correct way to do it (as, for instance, the non-arbitrary and universally true fact adding 2 to 2 gives you 4) ... rather, it's because that is now the governing convention in that context. (Indeed, it is the far more common convention now, precisely because of the prominence of computers as computational tools.)

This fact that this equation uses all numerals and no variables makes it particularly useful for revealing (and sowing, lol) this sort of distinction/argument. I think the ambiguity would be quite a bit clearer if the equation were written in variables. Now, everybody can agree that bc = b * c, right? But it is also absolutely true that bc = (b * c). So if you're given the expression a/bc, you've got an ambiguity problem, because it could be a/b * c or it could be a/(b * c).

jcgoldie

(11,631 posts)
97. Just to cherry pick one sentence...
Thu Aug 8, 2019, 02:59 PM
Aug 2019

"You can't really put the equation, as written, in most of the calculators or computers that kids would use for calculation, because doing so would require you to insert the operation symbol between two juxtaposed values after the slash. "

I realize this doesn't really address all your points but the fact is you can type it into any calculator that does order of operations correctly (ie "scientific&quot in exactly the way it is written and it will give you the answer of 16.

You can try it here:

https://www.meta-calculator.com/scientific-calculator.php?panel-201-calculator

I do not know how they wrote the language more than about 40 years ago when they wrote the textbooks I used in HS but I do know that there is a single right answer to the equation now the way it is written. If a student used the improper order in the midst of any of my classes from Algebra through calculus that I've taught I would have no problems subtracting points nor would I would guess (without evidence) 95% of HS mathematics teachers. Understanding rules of order of operations is rather basic to number sense and it is not arbitrary. I believe that you were agreeing with that and just arguing that symbols and how they are arranged to convey meaning is what you are calling arbitrary. That it is based in convention. I agree but I would also argue that we have to have some basic agreement over those principals or it would lead to serious problems in all sorts of applications.

Some here have said it would be clearer to add another set of parentheses around the first 2 terms. I agree with that as well and its a small joke I have told my students for years (which very few get) that "a LIBERAL use of parentheses in computation is almost always a good thing and wholly uncontroversial unlike in politics." When in doubt, add them. That being said, the extra parentheses would be redundant and do not change the meaning of the equation from what is written.

fishwax

(29,149 posts)
100. that's cool about the calculators
Thu Aug 8, 2019, 04:09 PM
Aug 2019

I don't really have a problem with you (or any other instructor) taking points off for a student getting the wrong answer, assuming they've been taught the convention. Mastering the convention is part of the point of the class. So they should be expected to execute whatever conventions have been adopted and conveyed. That's the point. Randos on the internet, though, not so much. Some of them might have simply been trained before java and google became the default. Or, they could be physicists or engineers, fields where the convention about grouping juxtaposed variables together remains very much in play.

Understanding rules of order of operations is rather basic to number sense and it is not arbitrary. I believe that you were agreeing with that and just arguing that symbols and how they are arranged to convey meaning is what you are calling arbitrary.

I think I agree with you here, but we may disagree on where the border between the two is. I mean, I think we could technically change the rules to the order of operations however we wanted and it wouldn't change the mathematical facts that the language of math describes -- but I agree as it relates to number sense and higher orders of operations. The levels of the order make perfect sense: if we didn't all agree to do exponents first than there wouldn't be much need for exponential notation, and the efficiency of exponential notation would be lost. Similarly, We don't *need* a multiplication operator, since any x * y can also be represented by x + x + x ... y number of times. But the multiplication symbol makes things easier, and so giving it precedence in the order of operations makes perfect sense.

The specific point as it relates to the order of operations in this equation, I believe, is whether ab = a * b or (a * b), and that's arbitrary. The "a * b" side has gained prominence in the past couple of decades because, well, that's what google says and what java says and what python says, and so that's the easier convention to follow. But that's just a programmed choice--there's nothing about it that is inherently right. It's just become the dominant convention, at least for simple calculations. When it comes to, say, engineers and scientists working with variables, I think one would still find a lot of people and texts treating ab as (a * b).

Anyway, this has been a fun conversation, and I'm all in for the liberal use of parentheses!

muriel_volestrangler

(101,320 posts)
134. No; putting it into my scientific calculator, using in place of /
Sat Aug 10, 2019, 05:04 AM
Aug 2019

(since it doesn't have the / sign), I actually get '2' on the screen. This is because on scientific calculators you should be putting in the multiplication symbol explicitly; without it, what it does is reject the first '2', and so works out 8÷(2+2) ; similarly, 8÷2(3+3) comes out as 1.33 recurring. And that brings us back to fishwax's point about juxtaposed quantities.

See https://math.berkeley.edu/~gbergman/misc/numbers/ord_ops.html (George Bergman, Dept of Mathematics, Berkeley)

Nay

(12,051 posts)
153. That's exactly what I did to get 1. The bar is a division bar, and
Sat Aug 10, 2019, 01:09 PM
Aug 2019

operations on the top or bottom of the bar would be done separately. Only then would you reduce the fraction to get your final answer.

LeftInTX

(25,364 posts)
150. The good old fraction bar!
Sat Aug 10, 2019, 12:48 PM
Aug 2019

Hard for a novice to format for use in MS Word!
8
2(2 + 2)

8
______
2(2 + 2)

Hotler

(11,425 posts)
51. Did'nt we haves this test a few weeks back?
Thu Aug 8, 2019, 09:52 AM
Aug 2019

Last edited Thu Aug 8, 2019, 10:36 AM - Edit history (1)

16
5 out 3 people struggle with math.

Afromania

(2,768 posts)
52. 8/2(2+2) 8/2(4) 8/8 1
Thu Aug 8, 2019, 10:12 AM
Aug 2019

I'm still trying to figure out how some folks are getting 16.

edit: I see it. my aging math mind refuses to believe it. Of course I was have math dyslexia... probably.

 

Joe941

(2,848 posts)
102. multiplication and division have the same precedence so go left to right...
Thu Aug 8, 2019, 04:34 PM
Aug 2019

8/2(2+2) = 8/2(4) = 4(4) = 16

LeftInTX

(25,364 posts)
159. It's newer notation
Sat Aug 10, 2019, 01:40 PM
Aug 2019

I have a degree in math from 1978 and I get 1 because we were taught that / was a horizontal bar over 2(2+2).

Also back then calculators couldn't do parenthesis etc.

Hotler

(11,425 posts)
56. People rember PEMDAS, but forget the rest of the rules of operation.
Thu Aug 8, 2019, 10:49 AM
Aug 2019

MD = Evaluate all multiplications and divisions as they occur in order from left to right.
AS = Evaluate all additions and subtractions as they occur in order from left to right.

It is easy to forget this tid bit of info.

kimbutgar

(21,155 posts)
57. Calm down everybody
Thu Aug 8, 2019, 11:28 AM
Aug 2019

I think the answer is 16 also.

But I also can see how one could come up with one if you look at 2 divided by 8. And not 8 divided by 2.

jcgoldie

(11,631 posts)
66. Its a math problem
Thu Aug 8, 2019, 12:52 PM
Aug 2019

There's only one answer. And the fact that there is so much disagreement a day after the rules have been explained gives one an idea of why a topic like politics which is full of gray areas could be so hard to reach consensus!

honest.abe

(8,678 posts)
59. An equation should never be written that way.
Thu Aug 8, 2019, 12:19 PM
Aug 2019

Its should be written like this:

(8/2) * (2+2)

So there is absolutely no confusion or debate about the stupid order of math operators.

 

not_the_one

(2,227 posts)
69. we should ALL demand non-ambiguous math!!!
Thu Aug 8, 2019, 01:13 PM
Aug 2019

I say we take it to the streets!!!

Imagine the protest signage. We would look EXACTLY like what we are... the educated elites (many who live on the coasts).

Ms. Toad

(34,074 posts)
70. (8/2) is redundant.
Thu Aug 8, 2019, 01:16 PM
Aug 2019

Multiplication and division have the same priority. Parentheses say: Do this first. Division preceding multiplication says: Do this first.

honest.abe

(8,678 posts)
73. A necessary minor redundancy to eliminate confusion like we see in this thread.
Thu Aug 8, 2019, 01:22 PM
Aug 2019

I am a programmer and parens are always used in cases like this to ensure clarity and reliability.

Ms. Toad

(34,074 posts)
104. I'm a programmer, as well,
Thu Aug 8, 2019, 06:33 PM
Aug 2019

and building in that redundancy (absent a linguistic requirement) does not match my experience.

honest.abe

(8,678 posts)
105. I suppose you could get away with it..
Thu Aug 8, 2019, 06:58 PM
Aug 2019

but I would never trust any code that was not clearly defined with parens that contained equations like this. A minor inconvenience to ensure clarity and accuracy.

Remember what is clear and obvious to you may not be to the next person editing your code.

Ms. Toad

(34,074 posts)
106. Any programmer
Thu Aug 8, 2019, 07:29 PM
Aug 2019

should understand 7th grade math**, not to mention that any programmer worth their salt also documents their code.

**I do come from the generation in which computer science degrees did not yet exist so most programmers majored in mathematics or physics.

From my perspective, adding unnecessary parenthesis is far more likely to make the code harder to read and to lead to coding errors - especially with a complex functions where one misplaced parenthesis out of the dozen or so in the funciton would be a beast to soft through for the error. Omitting redundant parentheses simplifies the error checking when the run produces an unanticipated result.

honest.abe

(8,678 posts)
110. Well we certainly see things differently.
Thu Aug 8, 2019, 07:49 PM
Aug 2019

My preference is to use both parens and comments to ensure clarity and understanding. If the equation is complex I would also use indenting and line spacing to help with readability.

Ms. Toad

(34,074 posts)
112. We do.
Thu Aug 8, 2019, 08:08 PM
Aug 2019

Indenting and line spacing don't helpwith locating the misplaced parenthesis that is messing with your results. So when the meaning is clear (i.e. 7th grade math rules), I want to remove extraneous characters that make it harder to debug.

honest.abe

(8,678 posts)
113. So those confused by this arbitrary math rule have less than 7th grade math skills??
Thu Aug 8, 2019, 08:30 PM
Aug 2019

Thats quite a broad and unfair insult.

Ms. Toad

(34,074 posts)
116. You seem to be confusing the level at which math skills are taught
Thu Aug 8, 2019, 09:25 PM
Aug 2019

with a judgment about whether people have, or have not, mastered a particuar skill.

When math skills are taught (X-grade math skills) is objective. It is not an insult to state the facts. (Although a quick google search suggests that the skill is now a 4th grade math skill - not surprising since math skills have progressively moved to lower grade levels to create enough room for 3 years of what used to be college level math in high school.)

I did say that I expected programmers to have mastered 7th grade math skills. I expect programmers to have better than average math skills given the nature of the reasoning required to program. It is also essential to their jobs to understand how a particular string of mathematical operations will be carried out by a computer - i.e. to understand that when told to calculate x/y*z the computer will divide first and then multiply.

FWIW, I expressly demanded that level of mathematical mastery from the 9th-12th grade students to whom I taught programming - and very few of them expected to earn a living as a programmer.

Ms. Toad

(34,074 posts)
124. It's still redundant,
Fri Aug 9, 2019, 07:36 PM
Aug 2019

And Google visibly demonstating the order in which it understands operations will be performed is significantly different from a programmer inserting parentheses whihc are operationally redundant - and which make it more likely that parentheses will be mismatched or misplaced causing computational errors that would not exist but for the insertion of redundant parentheses.

Aside from which - the fact that Google inserted them demonstrates there is no ambiguity as to the meaning of the phrase, confirming the fact that they are redundant.

I've spent way too much time debugging mismatched or misplaced parentheses to insert parentheses when they are redundant.

LeftInTX

(25,364 posts)
162. I had a degree in math from 1978 and I wrote programs as part of that degree
Sat Aug 10, 2019, 02:13 PM
Aug 2019

We had to write the programs to fit the notation of the day

So we would have written something like:
A = 2 + 2
B = 2 * A
C = 8/B

Ms. Toad

(34,074 posts)
163. Considerably different computing power in those days.
Sat Aug 10, 2019, 06:28 PM
Aug 2019

That was 1-2 years past the era when there was a single computer serving campus (the entire basement of the library) and I hoped I didn't trip on the way to the computer center with my massive box of punch cards - because if I put one of them back in out of order I had to wait 24 hours before I got my results to be able to fix the out-of-order run. About 4 years after a 4-function calculator cost ~ $100. 3-4 years before I was teaching programming still using dumb terminals and a punch tape - with one live phone link to a remote computer. Those were the days. Not.

But construction, particularly of longer functions, was particularly challenging because of limitations on both character count and computing power.

And - you really had to understand the order of operations to write it out that way!

hunter

(38,316 posts)
108. It's a grotesque thing.
Thu Aug 8, 2019, 07:41 PM
Aug 2019

Any hypothetical compiler that stumbled upon the programmer's intended meaning would reduce this text to a small integer constant, and then, if it was smart enough, would issue a Kevin compiler warning.




jmg257

(11,996 posts)
62. 16.
Thu Aug 8, 2019, 12:42 PM
Aug 2019

8/2*4

No distinction in order between multiplication and division - work left to right.

Punch into any AB CLX or PLC and they will confirm.

FakeNoose

(32,639 posts)
65. One
Thu Aug 8, 2019, 12:52 PM
Aug 2019

8 divided by 8 equals 1

The 2 + 2 operation is done first because it's in parentheses - and 2 times 4 is 8.

Rstrstx

(1,399 posts)
67. I hope the original problem looked more like this:
Thu Aug 8, 2019, 01:05 PM
Aug 2019

8
-- (2 + 2)
2

Perhaps DU can provide an "insert formula" button right after the "smilies"

jimmy the one

(2,708 posts)
74. You Tube explains it: both are, or were, correct
Thu Aug 8, 2019, 01:23 PM
Aug 2019

Our grandparents or ggparents would have been correct with '1', while today not so... well, listen & see:



I thought 1 myself; my integral & differential calculus & non euclid-geom helped me not a whit.

LeftInTX

(25,364 posts)
156. The Distributive Property gives me 1
Sat Aug 10, 2019, 01:31 PM
Aug 2019

Back in the day, my calculators didn't have parenthesis and could only do one step at a time... The were great for exponents...and difficult numbers, but a calculator for algebra!

Midnightwalk

(3,131 posts)
78. Don't be fragile
Thu Aug 8, 2019, 01:35 PM
Aug 2019

I would never trust a line of code that was so dependent on ordering rules. Another pair of parentheses would save me from figuring out if you meant what you wrote.

wryter2000

(46,051 posts)
79. How it's written is misleading
Thu Aug 8, 2019, 01:35 PM
Aug 2019

If everything to the right of the slash is the denominator, the answer is 1. If there's an asterisk like so--2*(2+2)-the answer is 16. Written out by hand, there would be no confusion about what is meant.

Never mind. My way is also ambiguous. Better explanations of why this is misleading can be found upthread.

Tommy_Carcetti

(43,182 posts)
83. My guess was 1
Thu Aug 8, 2019, 01:44 PM
Aug 2019

Simply because I immediately go for what is in parenthesis first.

For some reason I think that's how I was taught. But maybe it was wrong. We're talking decades now since I've had a refresher (although with my kids working their way up school, that will naturally work to help me reboot.)

SidDithers

(44,228 posts)
85. If it's ambiguous, then it's not a good mathematical question...
Thu Aug 8, 2019, 01:48 PM
Aug 2019

Math is a language, like any other. And the goal of any language is to communicate clearly and concisely.

A statement that isn't clear and concise, in math, is meaningless.


Is it (8/2)(2+2) = 16?
Is it 8/(2(2+2)? = 1?


Meaningless.

Sid

Mossfern

(2,511 posts)
87. Eight halves is 4
Thu Aug 8, 2019, 01:53 PM
Aug 2019

times 4
equals 16

Mommy math - did it intuitively because when I was in school we didn't have calculators.
Something must have been drilled into my head though.

Buns_of_Fire

(17,180 posts)
90. 42. Douglas Adams said it, I believe it, and that settles it.
Thu Aug 8, 2019, 02:16 PM
Aug 2019

Actually, I saw it as "1". As an ex-programmer, I would politely hand it back and ask for clarification before I committed it to running code.

DanTex

(20,709 posts)
96. A poorly written mathematical expression.
Thu Aug 8, 2019, 02:58 PM
Aug 2019

Not invalid, just poorly written. (8/2)(2+2) is much better. Technically, both are equal to 16, but really this is a sort of math version of "Buffalo buffalo Buffalo buffalo buffalo buffalo Buffalo buffalo."

 

2020Junker

(99 posts)
99. Reminds me of this classical Chinese poem
Thu Aug 8, 2019, 03:48 PM
Aug 2019

The entire poem is written with the shi sound, but because of how tonal the language is, it looks like a garbled mess even though you could totally parse it out according to grammatical rules.

https://chinesepod.com/blog/2014/10/25/how-to-read-a-chinese-poem-with-only-one-sound/

(Scroll down to the Pinyin version. It's hilarious)

Takket

(21,573 posts)
103. yeah the problem with this is...
Thu Aug 8, 2019, 04:38 PM
Aug 2019

any decent scientist/mathematician/engineer wouldn't be caught dead using the "divide" symbol, we use a slash / and we sure as hell also wouldn't be caught dead writing an expression with division in it on a single line. you always clearly build your numerator and denominator with everything "on top", horizontal bar, and everything "on the bottom".

they have a word for people who write ambiguous equations: Fired.

Recursion

(56,582 posts)
107. It's an ambiguous question, and depends on leftmost or rightmost binding rules
Thu Aug 8, 2019, 07:33 PM
Aug 2019

I find this question unbelievably uninteresting, but it keeps clogging my facebook feed.

lpbk2713

(42,757 posts)
111. Mr Cash would be proud.
Thu Aug 8, 2019, 07:51 PM
Aug 2019



My Ninth Grade Algebra I teacher.

I knew the answer before I opened up the OP.

NutmegYankee

(16,199 posts)
129. Technically it could be either as multiplication and division are equal.
Fri Aug 9, 2019, 09:49 PM
Aug 2019

But because we evaluate the equation from left to right, we get 16. In reality, it's a bullshit question because no mathematician would write an equation like this.

KY_EnviroGuy

(14,492 posts)
136. One
Sat Aug 10, 2019, 05:58 AM
Aug 2019

The math in the denominator must be completed before proceeding with the rest. Because there's no space between 2 and (2+2) in the denominator, that operation is done first so 2(4)=8, making the answer 1.

Rather than looking at it from left to right, see it as up and down like so:

8
--------- = 1
2(2+2)


KY......

muriel_volestrangler

(101,320 posts)
140. A counter-example to your interpretation comes from the Feynman lectures
Sat Aug 10, 2019, 09:16 AM
Aug 2019
With this interpretation 1 ÷ 2x is equal to (1 ÷ 2)x. However, in some of the academic literature, multiplication denoted by juxtaposition (also known as implied multiplication) is interpreted as having higher precedence than division, so that 1 ÷ 2x equals 1 ÷ (2x), not (1 ÷ 2)x.

For example, the manuscript submission instructions for the Physical Review journals state that multiplication is of higher precedence than division with a slash, and this is also the convention observed in prominent physics textbooks such as the Course of Theoretical Physics by Landau and Lifshitz and the Feynman Lectures on Physics.

https://en.wikipedia.org/wiki/Order_of_operations#Mixed_division_and_multiplication

See http://www.feynmanlectures.caltech.edu/I_06.html - it is written in one line as "within the deviation 1/2√N", and the full formula right after that is clear that it is

1
____
2√N

muriel_volestrangler

(101,320 posts)
142. Hmm, what do I consider more authoritative, Richard Feynman, or Excel?
Sat Aug 10, 2019, 10:02 AM
Aug 2019

Ooh, that's tricky, isn't it?

The point is that, as others such as fishwax above have said, the way it's written is ambiguous. Many mathematicians, and there are references in that Wikipedia article, and this thread, do say that implied multiplication (ie from 2 expressions placed next to each other, with no symbol - in this case '2' and '(2+2)' - does take precedence over division.

muriel_volestrangler

(101,320 posts)
145. Nobel.
Sat Aug 10, 2019, 10:17 AM
Aug 2019

One of the best teachers of physics there's ever been.

And, as I said, the point is that it can be interpreted in both ways. If your thought process is "if Excel interprets it this way, I must too", then you need to rethink your approach to life.

 

Trumpocalypse

(6,143 posts)
147. No Excel it the standard
Sat Aug 10, 2019, 10:20 AM
Aug 2019

Mathematics in physics is very different that ordinary mathematics. It is incorrect to apply those rules to a standard problem.

jcgoldie

(11,631 posts)
144. Except writing it with a fraction bar as you did...
Sat Aug 10, 2019, 10:17 AM
Aug 2019

...makes it a completely different expression. The (2+2) as written in the expression in the OP does not belong in the denominator at all.

There's a lot of debate here, but the rules for order of operations are very simple and straightforward. The ambiguity comes with either a too literal reading of the PEMDAS acronym causing people to prioritize multiplication over division which is incorrect or by making an assumption that you did that "/" should mean a fraction bar and everything after should be grouped. If we agree that is the case thats fine, but that is not the convention. Nor is the "implicit multiplication" that has been referenced here conventional in any modern arithmetic sense.

muriel_volestrangler

(101,320 posts)
146. No, implicit multiplication is conventional
Sat Aug 10, 2019, 10:20 AM
Aug 2019

That's the point. That's why it can be interpreted either way.

KY_EnviroGuy

(14,492 posts)
149. You hit the nail on the head. Conventions have changed.....
Sat Aug 10, 2019, 11:14 AM
Aug 2019

since the 60s when I had basic math, algebra and calculus. I solved the equation instinctively just as I would have in 1965, LOL.
In those days, we had no computers, calculators (that we could afford), smart devices or internet.

Some might see the OP format as potentially causing errors and prefer it be written (2+2)8/2 = 16, or we might have written it as 8/2 x (2+2) = 16 or for the other instance, 8/2 x 1/(2+2) = 1.

That points out the various profession's use of the multiply operand, whether to use "x" or "*" or "." (dot or asterisk vertically centered). In engineering we used the dot most times when everything was hand-written.

I didn't get to participate much in the "new math" my kids had because I was out traveling to pay the bills. I missed out on a lot in those days.......

Thanks for the interesting OP......

LeftInTX

(25,364 posts)
161. So in modern math what is
Sat Aug 10, 2019, 01:55 PM
Aug 2019

Last edited Sat Aug 10, 2019, 02:55 PM - Edit history (1)

20 ÷ 5x if x is 40?

is 20 ÷ 5x the same as
20/5x?

or
20/5*40?

honest.abe

(8,678 posts)
164. Interesting.
Sun Aug 11, 2019, 06:20 AM
Aug 2019

If written with a variable like 5x you have to do that first regardless of the order of operators rules. If no variable then the standard rules apply which would give you a much different answer.

Yes confusing which is why equations like this should always use parens to clearly define what should be done.

Throck

(2,520 posts)
154. 1
Sat Aug 10, 2019, 01:15 PM
Aug 2019

Last edited Sat Aug 10, 2019, 01:52 PM - Edit history (1)

Update: Just got schooled by a math teacher. 16 or 1 could be correct. She says it's a bastard equation with an undefined operator. The equation is solved like an array, hence two answers. I have been humbled.........again.

zipplewrath

(16,646 posts)
157. Poorly written equation
Sat Aug 10, 2019, 01:35 PM
Aug 2019

For any other purpose that trying to test a students ability to correctly deconstruct an equation, this is a horribly written equation.
Having spent a career expressing ideas and conveying instructions in equations, one would NEVER write it this way. Even in a piece of software, one would write it more clearly to reflect intent.

But furthermore, most equations are combinations of various "quantities" that represent something "physical" or an individual effect. So 8/2 might be a radius calculation. Or (2+2) might be a+b where both just happen to be 2. Or it could be that 8*(2+2) represents a whole quantity and we are looking for half of it. But whatever the case, I would write the equation to clearly show these relationships.

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