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

reply to post by GogoVicMorrow


Yes, but there are different perspective about it, so lets use common algo to express it - algebra.
If you think the answer is 288, please read my post here. Its algebra based solution with simple substitution for the proof of work.

Hi all.

I don't post much but am finding this thread very interesting.

I believe the answer to the problem, as presented is, 288.

Treating it as an algebra equation, without the express instruction to do so, is wrong. It could be computer code for all we know.
There are different methods of solving it depending on the context of its presentation. As presented the answer is 288.

adding in 0 = or Y = to make it an algebra equation is wrong and arbitrary.

Have a good day.

Edit
Common algo could be considered computer coding standards, which would absolutely give 288.

reply to post by safetyblack


because its maybe a computer code is the best reason to treat it as algebra.

For the laypeople....

From my limited experience and questions put to academics on the subject. Most confusion comes from shortcuts in writing. aka... being lazy.

" I cant be bothered to do it properly longhand " = " That's how its done ".


"Implied" is not a term that should be used in science. And yes it does have some physically negative outcomes. Especially in engineering.

Most programming languages will yield the result 288.

Go enter the equation in the box....48/2(3+9)

So Discovery Ed web math is wrong? I don't think so.

The orginal equation is proper.

48/2(3+9)=288

This Equation is proper.

(48/2)(3+9)=288

This equation is proper.

[(48/2)(3+9)]=288

This equation is proper.

48/[2(3+9)]=2

This equation is proper.

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

It doesn't matter if it's BODMAS, BEDMAS, PEMDAS. They all read left to right. The division has to be first. You get the answer 2, because you do the equation in your head properly, but write the equation wrong. Then you argue your written equation is right. LOL Seriously? Here's another website go to very bottom of the page and read the last equation 'Order of Operations'.
BODMAS

reply to post by GogoVicMorrow


Nope. I've got a degree in maths. You need to solve the brackets/parenthesis first. 2(9+3) simplifies to 2(12) not 2 x 12 - where no brackets/parenthesis are present, causing the mistake - so the denominator is 24, giving the answer 2.

Calculators can't do fuzzy logic. If you want to type it into a decent calculator (I use a Ti-89) you need to input 48/2[(9+3)] otherwise you're inputting nonsense and getting a nonsense answer.

reply to post by Arbitrageur


tried putting this through a compiler?

288 through a compiler as you have to apply multiplication to the expression to the right

We are discussing
48/2(9 + 3) as

48
------------
2(9 + 3)

right ?

or are we discussing

(48/2) x (9 + 3) ?

I'm really really confused why people accept 288 as the answer.

reply to post by NullVoid


Which of those two does 48/2(9+3) represent is the discussion.

reply to post by safetyblack


2(9+3) is one operator and must be solved first before you can move onto anything else.
48/2(9+3)
48/2(12)
48/24
2

The problem comes from computers not being able to put these abstract weightings on things and resorting to reading from left to right which gives the answer 288. You need to input the * to get the right answer - something that is much to the annoyance of people doing advanced algebra on them.

The real answer should be 'ask whoever wrote the sum which they meant'.

reply to post by bastion


I understand the methods of getting to both answers.

I do not believe this is algebra, as there is no variable. Simple arithmetic.

I do not think the denominator should be applied to the objects in the paren. if anything the whole fraction should.
((48/2 * 9) + (48/2 * 3))

reply to post by safetyblack


I can answer this simply. I've been teaching high school math for 8 years and I can assure you the answer is 2. Maths is a langauge and brackets have their own explicit function.

EC666
reply to post by safetyblack

 

I can answer this simply. I've been teaching high school math for 8 years and I can assure you the answer is 2. Maths is a langauge and brackets have their own explicit function.

Interesting. I think some of your students are here.

I appears that operator precedence, except in programming languages, is no longer clearly defined.

reply to post by safetyblack


LOL, NOW I think I understood the problem.

48/2(9+3) represent

48
-------------
2(9 + 3)
My take
Now, lets leave this to future generations shall we ?

reply to post by NullVoid

Drinks for the win!!!!

Here's my opinion: 3(5) = 3 * 5.

So...

48/2(12) = 48/2 * 12.

My opinion is this is easier to write: 48/2(9 +3)...

Versus: 48/(2(9 + 3)).

And this is easier to write: 3(3+5)...

Versus: 3 * (3+5).

So the convenience of writing the formula wins.

What's been proven here without a doubt (as if it needed any proof) is that if we leave any room for misinterpretation in our expressions, they'll be misinterpreted by man & machine alike.

Happens in all fields not just mathematics.

Pilgrum
What's been proven here without a doubt (as if it needed any proof) is that if we leave any room for misinterpretation in our expressions, they'll be misinterpreted by man & machine alike.

Happens in all fields not just mathematics.

Whew, lucky you said that early, I already prepare my pitchfork and torch already. I thought its mass hypnotic witchcraft of some sort, I'm really against witchcraft and number worshiping. How dare they say 888 is lucky number, dont they know about 911 ?

666/9*(11+1) = 888 - No, 888 is not lucky number, got some evil smells to it.

So, 288 people, it happen in all fields not just mathematics, so, I guess we are even, its already decided the answer is 2.

CthulhuMythos

James1982

AthlonSavage
reply to post by Arbitrageur

 

The general accepted rules of mathematics Multiplication, Division, addition and subtraction is that it occurs in that order. Therefore /2 operand takes place before 9+3.

Absolutely incorrect.

9+3 is in parenthesis, which means you absolutely must do the addition first.

Or you can distribute out the 2 over the parenthesis and get

48 divided by (18+6) which still gives you 24 on the denominator, and two as the final answer.

There is no debate here. 2 is the correct answer. The only debate is by people who forgot how to properly do math, or by people who don't realize calculators aren't perfect and you must be liberal with parenthesis to get the correct answer.

James1982

mojo2012
what is 48/2(x+y)? i typically assume that 48 is being divided by 2(x+y). I guess it should be written like this 48/[2(x+y)].

Great way of looking at it.

That would be 48/2x+2y

x=9
y=3

Then you get 48/18+6 or 48/24 or TWO.

I can't believe some people still think it's anything other than two. Sad state of education for sure.

That is exactly what I said. The two is a common factor of the elements of the sum within the brackets and so expanding will give you (18+6) which as brackets are solved first gives a denominator of 24. I see no ambiguity here.
original post

edit on 2-3-2014 by CthulhuMythos because: (no reason given)

I was supporting what you posted the last part was to those who still things is 288. Now after working the problem as a multiplication of the inverse I get 288, so I was being stupid in the first place.

I still can't find the illegal operation when getting 2, that's what's bugging me. If it's not 2, there should be an obvious illegal operation in the calculation to get 2, yet nothing seems to violate the laws.

Once you get to

48
-------
2(12)

If you were to solve that, what law makes multiplying the 2x12 first, illegal?

If there were variables involved

48
--------
2(x)

Your only choice is to divide first and then apply that value to the variable.

But if it's a known value, like 12 in this case, what law stops you from multiplying out the denominator before reducing the overall ratio?