Math question(simple)

[superman22x]

I just got told by an engineering student at Illinois Institute of Tech that the answer is two. I told him to drop out now before it's far too late.

 

[root]

My head said 288

PEMDAS
Parentheses
Exponent
Multiply
Divide
Add
Subtract


The Correct Answer Is 288

if you actually followed what you wrote verbatim then you'd have gotten 2. (which is the problem)
Parenthesis (deal with that first)
48 / 2 (9 + 3)
48 / 2 (12)

then you say mulitply

48 / 2(12) = 48 / 24

then you say divide
48 / 24 = 2

How did you use that magic order and not answer 2?

The trouble with your catchy mnemonic is that it doesn't adequately describe the various rules of maths.


so is the correct answer 2
48 / 2(9 + 3)
48 / 2(12)
48 / 24 = 2

or perhaps 288
48 / 2(9 + 3)
24(9 + 3)
216 + 72 = 288


or even 8.6 recurring?
48 / 2(9 + 3)
48 / 18 + 6
2.66666666 + 6
8.666666666

(I reckon 288)

 

[berry120]

For those that aren't clear with the reasoning - the key here is that operators of equal precedence (so divide, multiply and similarly for addition, subtraction) are evaluated left to right. Despite what PEMDAS, BODMAS etc. would have you think the D/M and A/S are actually on the same level. Apart from that as far as I know it's broadly correct.

So:

48 / 2 (9 + 3)

Brackets first, not much argument there. So we get:

48 / 2 * 12.

Since division and multiplication are of equal precedence we evaluate left to right, so the division comes first. We can thus rewrite the following expression like this:

(48/2) * 12

From then on it's easy, 48/2 gives us 24 and 24*12 gives us 288.

 

[superman22x]

It's gotten to 6 pages on the other forum, still people try and come in saying both 288 and 2 are correct or that 2 is correct. It's ridiculous.

I wrote a proof out for those old fools on the other forum, lol.

How about a proof?

48
--- * (9+3) = 288. Solve for x.
x

Step one, simplify.

48*(9+3)=576

576/x = 288.
576/288 = x.

x = 2.

Do the same thing but set the equation = 2.

48
--- * (9+3) = 2. Solve for x.
x

576/x = 2

x= 576/2

x = 288

So, if the answer was 2, the equation would look like

48÷288(9+3) = 2



And for those that think division should come before multiplication or vice versa, take a look at this:

48/2 = 48*(1/2)

 

[root]

that's not a proof.

I can write the same proof for the answer being two
48
---------- = 2 solve for x
x(9 + 3)

48
------- = 2
9x + 3x

48
--- = 2 therefore x = 2
12x


all these proofs (which would both be valid) shows is that the equation is badly written, and that causes confusion.

the point is unless the equation is re-written to be clear, then there is no real correct answer, there is a set of answers that are possible, numbers given above just happen to show those

 

[JogaBonito1502]

For those that aren't clear with the reasoning - the key here is that operators of equal precedence (so divide, multiply and similarly for addition, subtraction) are evaluated left to right. Despite what PEMDAS, BODMAS etc. would have you think the D/M and A/S are actually on the same level. Apart from that as far as I know it's broadly correct.

So:

48 / 2 (9 + 3)

Brackets first, not much argument there. So we get:

48 / 2 * 12.

Since division and multiplication are of equal precedence we evaluate left to right, so the division comes first. We can thus rewrite the following expression like this:

(48/2) * 12

From then on it's easy, 48/2 gives us 24 and 24*12 gives us 288.

Thank you! I don't know how this can even be a controversial topic. Pathetic. If you believe that the answer is 2 GTFO. Some operators do have equal priority which implies that you should evaluate them from left to right. The answer is 288. If you believe otherwise go back to 5th grade. There is no arguing and there is no rigorous proof that can be made. Just follow the mathematical rules. All there is to it.

 

[superman22x]

that's not a proof.

I can write the same proof for the answer being two
48
---------- = 2 solve for x
x(9 + 3)

48
------- = 2
9x + 3x

48
--- = 2 therefore x = 2
12x


all these proofs (which would both be valid) shows is that the equation is badly written, and that causes confusion.

the point is unless the equation is re-written to be clear, then there is no real correct answer, there is a set of answers that are possible, numbers given above just happen to show those

That's not the original equation.

 

[root]

That's not the original equation.

no, it's not, well, it is, and that's rather the point...

the original equation is

48/2(9+3)

[i'll write it as 48 / 2 * (9+3)]
now if you use the simplistic method (that's not correct) that first you have to deal with brackets,

48/2*12

then you use that same simplistic method that you have to deal with multiplication before division.
48/24

you get two...

if you ignore the mathematical mnemonic "rules" that were posted earlier and realise that multiplication and division actually carry the same preference then you read left to right.

then you get
48/2(9+3)
=48/2(12)
=24*12=288 (which is what I said in my first post, because I know that there are no preferences for multiplication over division).


so if you don't actually know how to do maths. then you deal with multiplication before division then you do
48
--- =2
2(9+3)

if you realise that multiplication has no preferential treatment then you read right to left divide 48 by 2, then multiply it by 12. (=288)

which is why I questioned how using his easy mnemonic xxpoweredgexx had managed to reach the correct answer, when if he'd played by the rules he's set out he should have performed the equation the way I'd written it.

basically, the way I wrote it was the original equation, if you follow an idiots guide mnemonic. the point of questioning your proof was that you wrote the equation how you (and i) read it, I wrote it how the people that are saying it equals two wrote it...

Basically, what I say to all those people who think it's two, I can understand how you think it's two, I can see why you think it's two. I can even write the equation showing the working, but you're still wrong.


or at least that's how I read it.

we could play this game forever.

1/2+4 = ?

is that

1
-- + 4 = 4.5
2

or
1
----- = 3
2+4

to my thinking, if I wrote the equation without brackets, then it's a little open to interpenetration.

if I wrote (1/2) + 4 or 1/(2+4) then it says what I mean...

should the original equation be written as

48/(2(9+3)) or (48/2)(9+3)


that's where the confusion for people is coming from.

 

[superman22x]

Whenever I write out equations for problems I am solving, they are as simply written as the one of the firs page. There is really nothing wrong with it. If you are seeing it a different way, you are either making assumptions or looking at it wrong.

 

[root]

Whenever I write out equations for problems I am solving, they are as simply written as the one of the firs page. There is really nothing wrong with it. If you are seeing it a different way, you are either making assumptions or looking at it wrong.

exactly.

Whenever you write equations that you are solving, you write them in a way that you understand, and you know what you mean...

other people may not. which is why it's important to be clear, and use brackets to signify intent when presenting something like that to somebody else other than you.

what's 1/2+3? that's all I'm giving you, I know what I mean in my head, and that's how I'd write that equation to give the answer that I'm thinking of...
but the intent that I have is ambiguous, without me putting brackets in to signify the intent it might be less clear to you... given that the notation is rather bland of formatting since it's written in plain in-line text.

you're going to have to make an assumption about what I mean.

if you don't get the answer that I (as the setter of the problem) think that you should get, does that mean that you're looking at it wrong, or that it's badly written?

(I'll give you a clue, it's badly written).