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48÷2(9+3) = ?

Reply 260

DanielleT192

13

Original post by HistoryRepeating

Thats just wrong on so many levels. Its frankly amazing that you think (x) functions different from x.

How is it wrong :s-smilie:

? Maybe the brackets aren't necessary in that case but I don't know how get the horizontal line, so the brackets were to make it easier to understand.

And brackets are sometimes necessary. Sure, in a simple case like this it's not necessary, i.e. 5(x) is the exact same as 5x, but 2x+6 is not the exact same as 2(x+6), which is what I mean by the initial question. When you've done a maths question, do you ALWAYS just start from the beginning, or do you have to work on one section and then do the question as a whole? This is the point I'm trying to make.

(edited 13 years ago)

Reply 261

Jingers

15

Original post by duck6

There is a lot of disagreement over the answer to this question so I though't I'd start a poll to see what everyone thinks

Lies. You just wanted to create a thread to see how many replies you get.

Reply 262

nuodai

17

Original post by Good bloke

Nobody could disagree with that, surely?

Indeed.

Up next: a poll on whether 18÷6÷3 equal to 1 or 9.

Reply 263

smiffhead

i can promise you this was all correct 6 years ago for a level maths, i can't find a source though and I have to go to work now.

Reply 264

asparkyn

15

It's not it's not! We learnt this in third grade --- brackets always come first, followed by everything else :sad:

48 / 2(9+3)

solve brackets

= 48 / 2(12)
= 48 / 24
= 2

I don't think I was cheated by my elementary school teachers! :nooo:

Reply 265

Good bloke

19

Original post by nuodai

Indeed.

Up next: a poll on whether 18÷6÷3 equal to 1 or 9.

I think, given the budget cuts and Portugal's problems, we should postpone that for a future programme.

Reply 266

py0alb

3

Original post by HistoryRepeating

Thats a completely different notation.

When using vertical fractional notation, vertical position effectively functions as parentheses.

That is simply not a function of using dash. 1/2 is not the same notation as

\frac{1}{2}

Even though in this instance they give the same result.

lol. Of course it is. It means exactly the same thing. and

2^{-1}

is also exactly the same thing. (you might not have come across that one yet)

Most undergraduates and above simply make the difference clear by spacing their formulas appropriately. Its perfectly fine to write:

x = 48/2 __ . __ (9+3)

I wouldn't mark down an undergrad who gave that as an answer.

Reply 267

IchiCC

12

This thread illustrates why I think schools should stop teaching mnemonics like BIDMAS. They just stir up a lot of misconceptions.

This question, strictly interpreted as written, gives the answer 288.

This is because

So we have

Brackets first:

Division and multiplication take equal precedence, so this expression would be evaluated left to right by convention*, so we have:

Which is 288. There is no argument about this, when we look at the question strictly as it is written.

*Not all mathematical operations are evaluated left to right, exponentiation for example is evaluated right to left.

(edited 13 years ago)

Reply 268

tripleeagle

11

My calculations and my calculator (http://www.wolframalpha.com/input/?i=48%C3%B72%289%2B3%29) agree that it's 288 :smile:

Reply 269

AidanKD

1

Oh dear...i'm sorry but...everyone whose insisting that this is 288...ARE YOU OUT OF YOUR MIND!?!? O,O

Break it up into it's sections...

the divide sign should seperate both sides so you know what would be on the top and bottom of the fraction for this division...

48

Divided by

2(9+3) --> 18 + 6 --> 24

48 divided by 24
=2

It's basic mental arithmetic is it really worth a 13 page debate? :s

No way in hell can I be convinced that this is 288 :P

Reply 270

orionmoo

15

As there is no second lot of brackets around the denominator, it is ambiguous what is being asked.
As it stands, using BIDMAS/BODMAS you get:
Brackets:
48÷2(9 + 3) = 48÷2(12)
Division:
48÷2 = 24 therefore = 24(12)
Multiplication:
= 288

That is the correct order of arithmetic, yes? Regardless of how a computer or calculator does them? It's like you put -2^2 into your calculator you get -4, when it's actually 4 - the calculator is only doing what you program it to do and if you don't tell it how to work things out in the correct order, it'll merely calculate them from right to left, as it does in this simple example.

The OP example is a very good reason why you should NOT write calculations involving fractions all on one line. As it stands, 288 is the correct answer based on how it is written, but I would say it's safe to assume that the calculation was originally intended to be

\frac{48}{2(9+3)}

and as such, in this case the answer is of course 2.

(edited 13 years ago)

Reply 271

DFranklin

18

I'd be fascinated to know how many people also think that

(-b +/- sqrt(b^2-4ac))/2a is the same as ((-b +/- sqrt(b^2-4ac))/2)a ...

Edit: or equivalently

(-b \pm \sqrt{b^2-4ac)}/2a = ((-b \pm \sqrt{b^2-4ac})/2)a

(edited 13 years ago)

Reply 272

Miss Anonymous

9

I say it's 2.

48/2(9+3)
= 48 / 18+6
(18+6 in the denominator)

= 48 / 24
= 2

Reply 273

Jallenbah

1

Original post by AidanKD

Oh dear...i'm sorry but...everyone whose insisting that this is 288...ARE YOU OUT OF YOUR MIND!?!? O,O

Break it up into it's sections...

the divide sign should seperate both sides so you know what would be on the top and bottom of the fraction for this division...

48

Divided by

2(9+3) --> 18 + 6 --> 24

48 divided by 24
=2

It's basic mental arithmetic is it really worth a 13 page debate? :s

No way in hell can I be convinced that this is 288 :P

the divide sign should seperate both sides so you know what would be on the top and bottom of the fraction for this division...

Where the hell did you get that? It's entirely wrong.

Reply 274

BJack

19

Original post by DFranklin

I'd be fascinated to know how many people also think that

(-b +/- sqrt(b^2-4ac))/2a is the same as ((-b +/- sqrt(b^2-4ac))/2)a ...

Are you trying to shirk your duties by making f38 explode? >_>

Reply 275

Jallenbah

1

Original post by orionmoo

As there is no second lot of brackets around the denominator, it is ambiguous what is being asked.
As it stands, using BIDMAS/BODMAS you get:
Brackets:
48÷2(9 + 3) = 48÷2(12)
Division:
48÷2 = 24 therefore = 24(12)
Multiplication:
= 288

That is the correct order of arithmetic, yes? Regardless of how a computer or calculator does them? It's like you put -2^2 into your calculator you get -4, when it's actually 4 - the calculator is only doing what you program it to do and if you don't tell it how to work things out in the correct order, it'll merely calculate them from right to left, as it does in this simple example.

The OP example is a very good reason why you should NOT write calculations involving fractions all on one line. As it stands, 288 is the correct answer based on how it is written, but I would say it's safe to assume that the calculation was originally intended to be

\frac{48}{2(9+3)}

and as such, in this case the answer is of course 2.

You realise splitting it up as a fraction onto multiple lines is identical to using brackets? There is no ambiguity here.

Reply 276

surina_xxx

i asked my mum, shes an A level teacher, the answers 2

Reply 277

Miss Anonymous

9

I think it's 2.
And so does my calculator
:wink:

Reply 278

smiffhead

Original post by IchiCC

This thread illustrates why I think schools should stop teaching mnemonics like BIDMAS. They just stir up a lot of misconceptions.

This question, strictly interpreted as written, gives the answer 288.

This is because

So we have

Brackets first:

Division and multiplication take equal precedence, so this expression would be evaluated left to right by convention*, so we have:

Which is 288. There is no argument about this, when we look at the question strictly as it is written.

*Not all mathematical operations are evaluated left to right, exponentiation for example is evaluated right to left.

but you can't use that identity at the top to imply anything about precedence.

Reply 279

Sovietpride

9

Original post by IchiCC

This thread illustrates why I think schools should stop teaching mnemonics like BIDMAS. They just stir up a lot of misconceptions.

This question, strictly interpreted as written, gives the answer 288.

This is because

So we have

Brackets first:

Division and multiplication take equal precedence, so this expression would be evaluated left to right by convention*, so we have:

Which is 288. There is no argument about this, when we look at the question strictly as it is written.

*Not all mathematical operations are evaluated left to right, exponentiation for example is evaluated right to left.

Whilst true, and i would, as i always did in gcse and a level, blame the question.
But, why have you have suddenly removed brackets?

I.e, you put 48 ÷ 2 x 12

When it still should have been

48 ÷ 2(12)

?

48÷2(9+3) = ?

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