Why you can't trust your calculator, or What is 48/2(9+3)?

reply to post by C0bzz


The problem is what it is. You solve it based on pemdas, not manipulate based on it.

reply to post by James1982


Its 288. Any college math class you go to will give you 288. You are applying incorrect attributes and/or changing the problem.
You do the addition first always as its in the parenthesis. Then you have 48/2·12.

So you are trying to sell us that 48/2·12 = 2? You are incorrect.

48/2 (9+3)
48/2·12
24·12
= 288

You and a few other is this thread are trying to manipulate the problem. Why? I dont know, its a very simple problem.

You always know there is a multiplication sign between a number and a parenthesis. You always solve a problem with division and multiplication in order (if there is no parenthesis).

So after you solve the addition in the parenthesis you have a simple division and multiplication job.

Anyone getting something other than 288 has forgotten basic math.. maybe because they've done too much math, I dont jnow, but regardless as to the reason, 2 is wrong. 288 is correct.

reply to post by GogoVicMorrow


It was solved using PEMDAS (not PEDMAS) using the method given by American Physical Society on page 1.

You are solving it either by placing Division before Multiplication or using the left-to-right method. I actually prefer the left-to-right method, I just don't know if it's any more correct than all the other ways of doing it which give a different result. I agree the answer is 288.

reply to post by C0bzz


That was a typo, obviously.

reply to post by C0bzz


You always solve division and multiplication in whatever order they come in.

reply to post by C0bzz


You guys seem to have forgotten. Maybe you are too far out of math, but despite the pedmas order of operations, there is an exception and that is that if you are down to multi and division you go left to right.

Every basic math book, teacher, and site will teach you this. Find me one place online that shows otherwise.

here you go

The M.D. in pemdas always says "multiplication and division go left to right"

I think the problem we have in this thread are that you and James and anyone else getting 2 have forgotten that M and D are interchangeable and go left to right. You just remember the acronym and have taken it literally.

reply to post by GogoVicMorrow

Every basic math book, teacher, and site will teach you this. Find me one place online that shows otherwise.

OK, the first post of this entire thread:

publish.aps.org...

reply to post by Arbitrageur


Also worth noting.. the older version hav the incorrect answer and the newer version (and every calculator after, every phone, every book, and every class) gives the correct answer of 288.

So, yeah, they fixed their calculator. Simple as that.

I got 2...

I thought things in brackets are sorted out first??

48 / 2 x (9+3)

48 / 2 x 12

48 / 24

2

reply to post by C0bzz


Want to point to the page in the file that says otherwise?

It doesnt change the absolute fact that all calculators and teachings since give the answer as 288 and the only one that doesnt is an older obsolete model of the same calculator that now gives the correct answer of 288.

I have shown you numerous times that multiplication and division are interchangeable according to the pemdas order of operations. You are taking it literal rather than how it is actually taught. I guess you are just one of those people that cant admit when they are wrong?

reply to post by iRoyalty


That is incorrect.
Things in parenthesis are sorted first but you go left to right when all you have left is multiplication and division. Its like 3rd grade math. Its a problem where people are taking pemdas too literally. Its just a tool to help students, its not a rule without exceptions. The M and D are interchangeable. When you only have the those left you go left to right.

link

For all the people that have forgotten. Pemdas (order of operations) has some exceptions. It is just a tool to help remember. It has exceptions. Those exceptions are that multiplication and division go left to right I'd they are the only signs left in the problem. Also the same goes for addition and subtraction, they go left to right.

PEMDAS:
Parentheses first

Exponents (ie Powers and Square Roots, etc.)

Multiplication and Division (left-to-right)

Addition and Subtraction (left-to-right)

reply to post by GogoVicMorrow


I see! It's been far too long since I've been at school lol

reply to post by GogoVicMorrow


Have you even bothered to read the thread, at all? Here's a diagram.



I can't admit I'm wrong when you're not properly responding to any information that has been posted. This is a communication failure on your part. Also I have already said that 288 is likely right, at least once in this thread, and I am now working on another post to justify that further.

reply to post by Arbitrageur


You are not interpreting the article properly.

The point of the article was that addition and multiplication have associative and commutative properties, so the order of doing multiplication and addition doesn't actually matter. Hence the distinction about either doing multiplication or addition left-to-right are not necessary to be taught because they do not matter. 1*2=2. 2*1=2.

Now obviously division is not the same in that way as multiplication. Order does matter, i.e. 1/2 is not the same as 2/1. But here is the key point in that document with regard to division.

Moreover, they also know that subtraction is the adding of a negative number and division by c is multiplication by 1/c.

math.berkeley.edu...

Hence another way to interpret the equation according to the paper is:

(48)*(1/2)*(9+3) = 288.

Check the end of page 5, because it gives a very similar example:

The example in (3) is perhaps a bit extreme, and was concocted to make a
point. However, the next one is taken from p. 207 of a school mathematics review
book [1]:

Evaluate 4 + 5 * 6 / 10.

Now one never gets a computation of this type in real life, for several reasons. In mathematics, the division symbol basically disappears after grade 7. Once fractions are taught, it is almost automatic that 6/10 would be replaced by 6*(1/10). Moreover, if anyone wants you to compute 4 + 5*6/10, he would certainly make sure that you do what he wants done, and would put parentheses around 5*6/10 for emphasis.

So according to your own source, the answer is 288.

If you don't replace division by c with a multiplication 1/c, as suggested in the article, then you end up having to go left-to-right to get the same answer. And that's the way pretty much all calculators do it, and they do it that way for a reason.

You also stated:

Multiplication and division can be similarly expressed so the order of execution makes no difference.

The only way you can possibly get 2 is if you use a specific order of execution by multiplying before dividing!

reply to post by C0bzz


No I didnt read the whole thread. I didny have to. I know the answer and a world of math agrees with me.

Nothing has shown me to be incorrect. That pdf doesnt apply. Someone is going way out of their way to cover their embarrassment of publicly answering a simple math problem wrong.

You state to me what the rule is and where you learned it prior to this vague pdf that you dont go left to right on multiplication and division and addition and subtraction when using PEMDAS?

Its all there on the internet. The only place its solved differently is on an old calculator and hasn't been solved as anything but 288 on any calculator since.

I can solve it on my phone and get (gasp) 288.

reply to post by C0bzz


Whats ironic is you are agreeing that the answer is 288 it seems, but where you are wrong is that PEMDAS is taken literally and doesnt give the answer of 288.

I do apologize because I thought you were agreeing with james that the answer was 2.

i think the confusion came from the difference between
48÷2(9+3)
and

48
---
2(9+3)

the first is 288
the second 2


48/2(9+3) looks like 48/(2(9+3))

The answer is 2.

Anyone typing that simple an equation into a calculator, that badly, deserves a wrong answer.

1/1(2+0)=0.5
or
1/1(2+0)=2
?
it depend on how the computer (human or machine) interpret /