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There is a huge debate on the internet on $48÷2(9+3)$. I figured if i wanted to know the answer this is the best place to ask.

I believe it is 2 as i believe it is part of the bracket operation in BEDMAS. http://www.mathway.com/ agrees with me. I also said if $48÷2*(9+3)$ was asked it would be $288$ which it agrees with as well. However wolframalpha says it is $288$ either way. A friend of mine (who is better at math) said theres no such thing as 'implicit multiplication', only shorthand so that is in fact done after the division (going left to right, not necessarily because division occurs before multiplication. But he didnt explicitly give a reasoning)

What is the answer and WHY?

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marked as duplicate by Arthur Fischer Mar 4 at 15:51

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I have never understood why one would want to establish arbitrary conventions on the order of operations. Just place appropriate parentheses and remove any ambiguity. Why would one ever want to write something like $5+8\cdot 6:4+3-2:5$? –  wildildildlife Apr 9 '11 at 15:34
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@wildildildlife: Well, the reason we put a convention on the order of operations is to make our life simpler. Not for problems like this, mind you, but for general expressions. E.g., if you had to write all the necessary parentheses every time you write out a polynomial, it would obscure things rather than clarify them. Instead of $2x^2+7x+1$, you would have to write$$\Bigl(2\bigl(x^2\bigr)\Bigl) + \Bigl(7x\Bigr) + 1.$$ –  Arturo Magidin Apr 9 '11 at 19:36
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«There is a huge debate on the internet»?! –  Mariano Suárez-Alvarez Apr 15 '11 at 21:27
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I must be crazy. I wasted 5 min of my life on this ... –  GWu Apr 15 '11 at 21:59
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I voted to reopen. I don't see why this is not a real question. The fact that someone picked it up as a meme on the net and wrote "there's a huge debate on the internet" doesn't make the question whether division or multiplication takes precedence here invalid; this is a perfectly legitimate question about mathematical notation. –  joriki Feb 25 '12 at 17:22
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4 Answers 4

There is no Supreme Court for mathematical notation; there were no commandments handed down on Sinai concerning operational precedence; all there is, is convention, and different people are free to adhere to different conventions. Wise people will stick in enough parentheses to make it impossible for anyone to mistake the meaning. If they mean, $(48\div2)(9+3)$, they'll write it that way; if they mean $48\div\bigl(2(9+3)\bigr)$, they'll write it that way.

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+1 Well said . . –  Bill Dubuque Apr 16 '11 at 2:18
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Recommended reading on this topic: "Order of operations" and other oddities in school mathematics by Hung-Hsi Wu, a Berkeley mathematician who has given much thought to mathematics education. –  Bill Dubuque May 4 '11 at 14:30
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My teacher adheres opposite to the convention I like. And she writes it so that there's ambiguity, resulting in rare "mistakes" on my part. Whenever I see $48÷2(9+3)$, I automatically think $2$. –  muntoo May 7 '11 at 0:01
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I don't agree with this type of answer: even if this expression is written by mixing old style symbols and new style ones, you cannot let the idea that you can evaluate an expression by your mood, or convention. There is ONE convention which should be agreed on by any mathematician: multiplication and division have the same precedence. –  Emanuele Paolini Oct 14 '13 at 5:35
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@EmanuelePaolini: "ONE convention which should be agreed on by any mathematician"? I think the problem is exactly the fact that most mathematicians don't use the $\div$ sign, so (from lack of use) we haven't really agreed on a convention. (In fact, just to write that sentence I had to look up how to write $\div$ in TeX because I never use it.) –  Jesse Madnick Mar 4 at 13:58
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It's ambiguous, there is not one right answer in this case, other than possibly that it is undefined. You may have $$\frac{48}{2(9+3)} = 2$$
or
$$\frac{48}{2}(9+3) = 288$$

Therefore, there is no point in debating this.

Note that the reason you are get different answers from mathway and google calculator is that the algorithms they use for parsing input are different. These algorithms apparently (and understandably) leave it up to the user in this case to give input that can only be interpreted in one way. This is not the case, and is therefore why the two's answers differ.

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Is there nothing that says if "2(" is part of the bracket operation or not while doing order of operation? If not then i'll agree. –  acidzombie24 Apr 15 '11 at 21:42
    
@acidzombie24: No, there is not. The standard notation to use in this case if you are going to use brackets is to use "fractions" rather than $÷$, as shown. Hope this clears things up =D –  fdart17 Apr 15 '11 at 21:44
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I would say it isn't even well-defined. In Group Theory or such, you usually pass by a statement that says "associativity means that $(1 + 2) + 3$ is the same as $1 + (2+3)$, so we can write $1 + 2 + 3$ without ambiguity." $÷$ doesn't have this property of not being ambiguous.

This is one of the advantages of using $\frac{48}{2}(9+3)$ or $\frac{48}{2(9+3)}$ - it's not quite associative, but it isn't ambiguous. I haven't seen $÷$ since elementary school probably for this very reason.

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And personally, I like to think of the obelus as a symbol meaning that "something" goes on top and bottom of the line, and the dots are just placeholders for the things on the left and right. –  Joe Z. Apr 2 at 4:00
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There is no order difference between implicit and explicit multiplications. Purplemath suggests that implied multiplication outside of parentheses also gets parenthetical order priority over all other multiplication(division). So they would interpret the implied multiplied parenthetical as $48\div(2\times(9+3)) = 2$.

Alternatively, all implicit-capable calculators I've tried give the same results as Wolfgram Alpha which interprets the implication as $(48\div2)\cdot(9+3) = 288$

Some confusion also seems to be the $\div$ division symbol itself as $48/2(9+3)$ visually supports the mutual parenthetical implied multiplication of Wolfgram Alpha: $\frac{48}{2}\cdot(9+3) = 288$

The short answer is that the formula as written is too easily misinterpreted and the author should clarify it to ensure its proper calculation.

PS: to further furrow your brow - employing the parenthetical as a variable yields different results. So, $48\div2c$ where $c=9+3$ yields $2$ - but this conflates the distinction from parenthetical to coefficient-variable syntax. $48\div2\cdot c$ where $c=9+3$ yields $288$.

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protected by J. M. Jul 28 '12 at 1:09

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