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Geek Culture / Solve this problem

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Phaelax
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Posted: 22nd Apr 2011 17:18
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48÷2(9+3) = ?

Ok, we have a page long discussion on FB about the correct answer to this. I say it\\\'s 288 if you follow (properly!) the order of operations, while many others (including a supposed calculus teacher) claim the answer is 2.

What do you guys think?

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mr_d
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Posted: 22nd Apr 2011 17:41
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i agree with you - it's 288

() first, ÷ second, and * last (as ÷ and * have same order of precedence and is hence calculated from left to right).

i.e. 48÷2*(9+3)=48÷2*12=24*12=288

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Gencheff
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Posted: 22nd Apr 2011 17:51
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I agree ,it's 288.


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thenerd
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Posted: 22nd Apr 2011 17:55 Edited at: 22nd Apr 2011 17:55
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48÷2(9+3)
48÷2(12)
48÷2*12
24*12
288
[b]

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Indicium
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Posted: 22nd Apr 2011 18:09 Edited at: 22nd Apr 2011 18:18
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Same process as thenerd here.

Also, Darkbasic agrees.

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AndrewT
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Posted: 22nd Apr 2011 18:16 Edited at: 22nd Apr 2011 18:16
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Technically yeah I think it should be 288. But I can see how someone might accidentally interpret it differently, because of the way you write "2(9+3)" rather than "2*(9+3)". For instance if I write -b/2a I think a lot of people might (understandably) interpret that as -b/(2a), rather than (-b/2)a, which is how technically should be interpreted.

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Syncaidius
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Posted: 22nd Apr 2011 18:17
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Same workings as thenerd.

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thenerd
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Posted: 22nd Apr 2011 18:40
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I'm surprised that a teacher got a different example, because it is a pretty much universal algebraic concept that parentheses are used in the place of multiplication symbols. At least, that's how I learned it...

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Interplanetary Funk
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Posted: 22nd Apr 2011 19:20
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Don't people on FaceBook know about BIDMAS?! This is how the world will end...

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bitJericho
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Posted: 22nd Apr 2011 19:29 Edited at: 22nd Apr 2011 19:31
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Yeah it's 288. You complete the parenthesis and then complete division and multiplication from left to right. Division and multiplication have the same order of operation.

Quote: "or instance if I write -b/2a I think a lot of people might (understandably) interpret that as -b/(2a), rather than (-b/2)a, which is how technically should be interpreted."


I don't think anyone would interpret it like that unless they were poor at math or just made a mistake that they would realize if they spent time on it.

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Diggsey
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Posted: 22nd Apr 2011 22:13
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It doesn't matter what it is, it shouldn't be written like that If you omit multiplication signs you should show division by a horizontal line.



[b]
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Lost in Thought
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Posted: 22nd Apr 2011 22:27
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They taught us all through school that mult comes before div. PEMDAS. So it all depends on how you were taught I guess. In which case the answer is 2.

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Teh Stone
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Posted: 22nd Apr 2011 22:43
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Yeah but doesn't the BRACKETS part of bidmas also include expanding out the brackets...
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Indicium
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Posted: 22nd Apr 2011 22:50
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Quote: "Yeah but doesn't the BRACKETS part of bidmas also include expanding out the brackets..."


No.

Now that I think about it, I completely agree with Diggsey, I can't remember the last time I used a division sign.

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Neuro Fuzzy
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Posted: 23rd Apr 2011 00:15
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48÷2(9+3)

The question is whether it evaluates to this (in RPN)

* ÷ 48 2 + 9 3

or this:

÷ 48 * 2 + 9 3

I'd say with the algorithmic approach of "PEMDAS", evaluating the equation looks like this:


48÷2*12 //Parentheses first
48÷24 //then multiplication
2 //then division.


Errm, but as someone who's into computers, I'd say that writing the equation like that in the first place is stupid! Graphing calculators evaluate the statement to 288, and so does wolfram alpha, while the main "PEMDAS" approach (my class was taught that in teh USA/CA at least) shows that the answer is two!

If I want something to be calculated exactly how I say it should be, then RPN or many parentheses is the way to go.

(or writing it out on paper, so you have horizontal lines n stuff)


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Phaelax
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Posted: 23rd Apr 2011 00:23 Edited at: 23rd Apr 2011 00:48
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I just wrote the equation how she wrote it.

Quote: "They taught us all through school that mult comes before div"

Pretty sure division and multiplication are the same level and thus done from left to right. Unless you're in Australia, then everything goes in the other direction like a toilet.

As amber put it, she "math rolled" us. Which I still don't understand what's so funny about it.
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Happy Cheesecake
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Posted: 23rd Apr 2011 01:23
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PEMDAS is kind of taken the wrong way sometimes. It's actually PE(M or D)(A or S). Like mentioned earlier, I believe, if there is both multiply and divide in the same problem, it is done from left to right.

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Tiborko
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Posted: 23rd Apr 2011 01:24
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this is not worth discussing...
48÷2(9+3) is the same as (48/2)*(9+3) and it's 288.
it can only be 2 if it was written like this: 48÷(2(9+3)) and it can't be the other way. conversation over :p

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mr_d
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Posted: 23rd Apr 2011 11:09
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Quote: "Pretty sure division and multiplication are the same level and thus done from left to right. Unless you're in Australia, then everything goes in the other direction like a toilet."


@Phaelax
Don't know if this was supposed to be a joke only, half a joke, or fact, but it's untrue either way, we do the same type of maths as the rest of the world (or maybe not considering the arguments this has raised with PEMDAS, BIDMAS, or even RPN - yer gotta love those Polish ).

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Thraxas
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Posted: 23rd Apr 2011 11:17
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Quote: "Don't know if this was supposed to be a joke"


Yes a joke, based on the idea that water goes down the drain in a different direction based on what hemisphere you live in.

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Phaelax
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Posted: 23rd Apr 2011 11:19
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It was a joke. You never heard that the toilet water spins the opposite direction when flushed in Australia? (I know its not true)

Some languages read right to left, so I wonder if its confusing to them to do math left to right?

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Lost in Thought
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Posted: 23rd Apr 2011 12:18
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I'm serious. They actually taught us all through school that you literally followed PEMDAS. You are correct in that the answer should be 288. The MD and AS are supposed to be equals to each other. And it is supposed to be worked left to right. I was only explaining why they got 2. The problem is that teachers don't really understand what they are teaching. They just read one sentance in the book and tell it to the students line by line.

They literally taught us to do that problem 48÷2(9+3):

() first so it's now 48÷2*12
* next so it's now 48÷24
÷ next so it's 2

And they are teaching it incorrectly this way all over the US which is why so many people got it wrong. Our education system sucks.

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Phaelax
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Posted: 23rd Apr 2011 13:33
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I think maybe the only reason I know better is because I got into programming. But if you look at the link I posted, it shows pictures of some calculators getting the wrong answer as well.

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