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48÷2(9+3) = ????

Discussion in 'BBS Hangout' started by Pull_Up_3, Apr 7, 2011.

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PEMDAS

  1. 288

    48.9%
  2. 2

    46.2%
  3. idunnololdog.jpg

    4.9%
  1. brantonli24

    brantonli24 Member

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    Division is not associative (changing the brackets do matter), for example:

    (12/6)/2 = 1

    but

    12/(6/2) = 4

    Unlike multiplication (and addition)

    (12*6)*2 = 144
    12*(6*2) = 144

    Imagine this:

    2-3+5 = ?

    You DO NOT do
    2-(3+5) = -6

    You do:
    (2-3)+5 = 4

    The sign in front of the number matters.

    I fell into the trap the first time, but now that I think it through, it's clear. Imagine it as a fraction.

    [​IMG]
    (I hope this works)

    The left one is represented by

    48÷2x(9+3) = 288

    The right one is represented by

    48÷2÷(9+3) = 2

    See?

    So the answer is 288.

    *note I'm just a high school student, so feel free to ignore me.
     
    1 person likes this.
  2. srrm

    srrm Member

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    ^^^^^^^^^^^ YES. brantonli24 got it

    That's the clearest explanation possible:

    you get the answer 2 by thinking of it as: 48÷2÷(9+3) = 2

    which is not what the question asks since there is no second division sign. It is instead multiplication
     
  3. freemaniam

    freemaniam 我是自由人

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    Agree with you here. I have suggested a bad example.

    [Edit] I knew the trap as I have said earlier. What I was trying to explain was that I (and perhaps the other who got the answer 2 as well) was accustomed to look into values within a parenthesis as a "package deal" (thank you H-townhero's link for the buzz word), so (9+3) as (a), also, a value placed immediate left of the "package deal" as the "coefficient", i.e. the multiplier "2" here. As a result, 2(9+3) was conveniently denoted as 2(a) hence 48÷2(a)=48÷2a. I was advised or directed to links with explanations of "order of operations" and I am grateful of that but all of the samples within were clearly illustrated with the multiply sign, i.e. an "X" or "*". I have no problem 48÷2x(9+3)=288, this is simple arithmetic and no argument at all. But the original formula was 48÷2(9+3) and team-288 here automatically assumed 48÷2x(9+3), I'm sorry but so far I was not enlightened any mathematical fundamental or rules where team-288's conversion would apply.

    [Edit Edit] Okay, I think I see the flaw in my explanation above. I mean 48÷2(a)<>48÷2a but=24(a). I am convinced it should be 288.
     
    #383 freemaniam, Apr 8, 2011
    Last edited: Apr 8, 2011
  4. madmonkey37

    madmonkey37 Member

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    Hopefully when I wake up tommorow this place will have a higher percentage choosing the right answer (288) than grasscity.com
     
  5. H-townhero

    H-townhero Member

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    Indeed, grammar nazi feel.. I too go for parenthesis first because of integrals/derivatives but the fact of the matter is ambiguity in equations like this are possible, and to solve ambiguity they go from left to right.

    I don't think I've seen a poorly written equation like this in any of my calculus books though, they always use plenty of brackets. :p (either that or my memory is horrible!)
     
  6. freemaniam

    freemaniam 我是自由人

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    Great elaboration.
     
  7. eMat

    eMat Member

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    So the intelligence of the average clutchfan seems to be higher than that of the average bodybuilder or pothead.

    Barely.

    First time I hear any "multiplication before division" or "addition before subtraction" BS. Left to right, it's as simple as that.
     
  8. SuperHighFly

    SuperHighFly Member

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    Wow I can't believe there's actually 20 pages on this. When I first saw it, I thought whats there to even argue, but wow.
     
  9. Turpis

    Turpis Member

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    I got 288, and was like WTF with people choosing 2, so went over to wolfram (who made mathematica program btw)...

    [​IMG]
     
  10. sammy

    sammy Member

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    I have doctors on my facebook status that got 2. They're so arrogant LOL
     
  11. wizkid83

    wizkid83 Member

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    The two is out side of parenthesis. Solve everything in parenthesis and you get 48/2*12 which you solve left to right and get you 288.
     
  12. wizkid83

    wizkid83 Member

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    Just got to quote this for anybody still arguing against it.
     
  13. tingYAO

    tingYAO Member

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    No Dakota, you FOOL.

    That is WRONG!!!
     
  14. Pull_Up_3

    Pull_Up_3 Member

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    lol wow
    ok people its very simple

    48/2(9+3)

    first parentheses (9+3)=12

    Your parentheses is gone now so it becomes multiplication

    48/2*12

    now you multiply or divide from left to right whichever comes first


    48/2=24

    now 24*12=288
     
  15. DonkeyMagic

    DonkeyMagic Member
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    a lot of posters have been knocked down a notch with some of their replies in this thread.

    i wee for the future.

    [​IMG]

    and the past for some of the older posters.
     
  16. tinywang

    tinywang Member

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    Everyone just needs to agree that:
    48÷2(9+3) = 48÷2*(9+3)

    48÷2*(12)

    Why does 12 need parentheses??? IT DOESN'T, it's not any more special than 48 or 2.
     
  17. brantonli24

    brantonli24 Member

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    I think it did, in order to draw people's attention to it and away from the ÷. So your first instinct would be to do the bracket, and then you see the 2 and multiply it, and then have 48 divide it. That may well be one of the reasons why it has managed to fool so many people.
     
  18. bobrek

    bobrek Politics belong in the D & D

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    EDIT: Never mind, I misread this....
     
    #398 bobrek, Apr 8, 2011
    Last edited: Apr 8, 2011
  19. hotblooded

    hotblooded Member

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    I did quant in uni answer is 288. The rest of you. It's not that a big deal you got it wrong The equation is not vague at all but sometimes maths is just like that , it confuses people
     
  20. candlegreen

    candlegreen Member

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    I just think it's funny that there's a 20 page thread on this....

    And yes, it's 288....
     

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