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I am confused

Started by Adrian K, Apr 28 2011 06:31 PM

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13 replies to this topic

#1 Adrian K

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Posted 28 April 2011 - 06:31 PM

Recently there was a debate in a Malaysian forum (forum.lowyat.net) regarding the mathematics:

48÷2(9+3) = ?

Some answers 2, and some answers 288

There are lots of trolls or keyboard heroes in that forum, I don't really trust their answer, that's the reason I come to ask you guys. Most of them answers 288.

I am really confused. My answer is 2, this is killing me.

p/s: some other forum mentioned they use mathlab and got 288?

Edited by adrian kohsf, 28 April 2011 - 06:33 PM.

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#2 lab rat

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Posted 28 April 2011 - 06:39 PM

I get 288 Adrian, both by calculator and excel.

First I did parenthesis: 9+3 = 12
Then I did the equation in order: 48/2 = 12 * 12 = 288.

Insert a multiple operator between the 2 and the parenthesis, and you'll see why I got this.

42..."An immutable fixed-precision number of unlimited magnitude." <a href="http://en.wikipedia....amming_language)" target="_blank">http://en.wikipedia....amming_language)</a>, accessed 25June2009.

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#3 lab rat

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Posted 28 April 2011 - 06:43 PM

And what is a 'keyboard hero'?

42..."An immutable fixed-precision number of unlimited magnitude." <a href="http://en.wikipedia....amming_language)" target="_blank">http://en.wikipedia....amming_language)</a>, accessed 25June2009.

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#4 laurequillo

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Posted 28 April 2011 - 08:09 PM

I like better trolls!! :lol:

yeah for me it is 2 as well. I first do (9+3) then 12*2= 24 (that should be the order) and then 48/24=2 .
The 288 is just because the treat the parentesis as if it were multiplying 48/2 so
48/2 * (9+3)

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#5 lab rat

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Posted 28 April 2011 - 08:26 PM

I made a typo in my post, I meant to say 48/2 = 24.

I don't know, LQ. Isn't it supposed to be the sum inside the parenthesis, then the multiplication and division starting at the left?

It's good there isn't an exponent in here, or we'd all be sunk. :lol:

42..."An immutable fixed-precision number of unlimited magnitude." <a href="http://en.wikipedia....amming_language)" target="_blank">http://en.wikipedia....amming_language)</a>, accessed 25June2009.

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#6 Ameya P

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Posted 28 April 2011 - 09:04 PM

Adrian,

it will be 288 ..... Brackets first, then division and then multiplication. (Using BODMAS)

If you use BOMDAS/ PEMDAS (as called in the US) then the answer is 2.

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#7 pito

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Posted 29 April 2011 - 12:53 AM

I knew I studied math for a reason, finnaly I can use my math skills:

48÷2(9+3) = ? you do mean that there is a "multiply sign" between the 2 and the ( ?

If so the answer is: 24 . 12 or 288.

And the rules are: Brackets first and dividing/multiplying are on the same "level" , meaning this case you go from right to left, so first dividing and then multiplying.

As some others allready mention.

To give you all the rules:

levels are : 1. Brackets, 2. Exponentiation, 3. dividing/multiplying, 4. + and -

And those are the levels.. so brackets comes first then... and when two on the same level: work from left to right (first comes, first served :lol:

).

Edited by pito, 29 April 2011 - 02:48 AM.

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#8 gebirgsziege

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Posted 29 April 2011 - 01:14 AM

Pitos explaination is excellent. The answer would only be 2 if the equation is written:

48/[2*(9+3)]

otherwise the calcualtion must be read as function 1 [48/2] * function 2 [(9+3)]

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#9 hobglobin

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Posted 29 April 2011 - 02:27 AM

google gives the right answer, just try out...

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...except casandra's that belong to the funniest, most interesting and imaginative (or over-imaginative?) ones, I suppose.

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#10 Adrian K

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Posted 29 April 2011 - 02:40 AM

Ops, should be "Keyboard Warrior" rather than "keyboard hero", my bad...

I had actually thought, by replace the 2 with A:
48÷A(9+3) = 48÷(9A+3A)= 48÷(12A) =4/A, replace A with 2, got 2 as answer...

This is because I thought (was taught) if the multiply operator was not there (as in this case), we should be given the priority to solve it first?

Exactly Geb, if the equation was written as 48÷[2 X (9+3)], the answer is 2. That's why I am confused...

Anyway guys, thanks for the clarification.

Expecting the world to treat you fairly because you are a good person is like expecting the lion not to attack you because you are a vegetarian.

..."best of our knowledge, as far as we know this had never been reported before, though I can't possible read all the published journals on earth, but by perform thorough search in google, the keywords did not match any documents"...

"what doesn't kill you, makes you stronger"---Goddess Casandra reminds me to be strong

"It's all just DNA. Do it."---phage434

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#11 pito

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Posted 29 April 2011 - 02:53 AM

adrian kohsf, on 29 April 2011 - 02:40 AM, said:

Ops, should be "Keyboard Warrior" rather than "keyboard hero", my bad...

I had actually thought, by replace the 2 with A:
48÷A(9+3) = 48÷(9A+3A)= 48÷(12A) =4/A, replace A with 2, got 2 as answer...

The problem is that you can NEVER do this.

"the rule" in math is that brackets come before all the rest.. no matter whats writting next, above or... it.

Always go for the brackets first, then you can not make any mistake.

And then you follow the other rules...

BTW: is it normal not to write the "multiplying operator" ? I have always been told to write the X or . so how come it not here?
Because writing nothing could mean anything => to me it just means that the one who wrote it missed an operator so it could be anything from ^, x, to ln ...

hobglobin, on 29 April 2011 - 02:27 AM, said:

google gives the right answer, just try out...

it sure does :lol:

If you don't know it, then ask it! Better to ask and look foolish to some then not ask and stay stupid.

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#12 Ameya P

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Posted 01 May 2011 - 09:17 PM

hobglobin, on 29 April 2011 - 02:27 AM, said:

google gives the right answer, just try out...

Hobglobin, Wonder what your kids are going to do in School :lol:

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#13 newborn

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Posted 01 May 2011 - 10:06 PM

I agree with the rule as Pito pointed, you cannot analyze that way. It should be

48÷A(9+3) = (48/A)(9+3)= 12*(48/A), replace A with 2, you will get 288.

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#14 hobglobin

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Posted 02 May 2011 - 05:48 AM

gt_ameya, on 01 May 2011 - 09:17 PM, said:

hobglobin, on 29 April 2011 - 02:27 AM, said:

google gives the right answer, just try out...

Hobglobin, Wonder what your kids are going to do in School :lol:

luckily I have no kids...

but google shows the way to calculate it, this way: (48 ÷ 2) * (9 + 3) = 288
should be explanatory enough....

One must presume that long and short arguments contribute to the same end. - Epicurus
...except casandra's that belong to the funniest, most interesting and imaginative (or over-imaginative?) ones, I suppose.

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