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Lame ass maths riddle

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  • 20-04-2011 11:21pm
    #1
    nyarlothothep
    Registered Users Posts: 5,176 ✭✭✭


    What is 30÷2(2+3)÷5

    Is it 15?

    or 0.6?
    ...
    Or is this question broken?


«13

Comments

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    #2
    hondasam
    Closed Accounts Posts: 34,419 ✭✭✭✭hondasam


    I Don't understand the question


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    #3
    nyarlothothep
    Registered Users Posts: 5,176 ✭✭✭nyarlothothep


    Well what does the equation equal? Or is there something wrong with it?


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    #4
    [Deleted User]
    Posts: 0 ✭ [Deleted User]


    Isn't it 15?

    30 divided by two

    equals 15

    2 plus three equals 5

    15 multiplied by five equals 75

    75 divided by five is fifteen.

    No? It's been a while since I was in school, but I thought that was the way it worked


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    #5
    Cavehill Red
    Registered Users Posts: 6,109 ✭✭✭Cavehill Red


    It's 30 over the 2(2+3) over 5.
    So that's 30 divided by (2X5) divided by 5.
    Which is 30/10 divided by 5.
    Which is 3/5 = 0.6.


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    #6
    JBnaglfar
    Registered Users Posts: 841 ✭✭✭JBnaglfar


    ^^ I got that at first.

    If you want to get 15 you can.

    2(2+3) divided by 5 = 2
    30 divided by 2 = 15.

    This is basically asking 30 divided by 10 divided by 5, and I didn't think maths necessarily went from left to right.

    Edit: google suggests .6 is correct
    link


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    #7
    nyarlothothep
    Registered Users Posts: 5,176 ✭✭✭nyarlothothep


    I love troll maths


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    #8
    mari2222
    Registered Users Posts: 568 ✭✭✭mari2222


    it is 15. to get the answer .6 you would need another set of brackets within the equation.


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    #9
    nyarlothothep
    Registered Users Posts: 5,176 ✭✭✭nyarlothothep


    Here's another one

    -20=-20
    16-36=25-45 (16-36=-20,25-45=-20)
    4^2-36 = 5^2-45 (4^2=16,5^2=25)
    4^2-36 = 5^2-45
    4^2-2.4.9/2 = 5^2-2.5.9/2 (2.4.9/2=36,2.5.9/2=45)
    4^2-2.4.9/2 +(9/2)^2 = 5^2-2.5.9/2 +(9/2)^2 (adding both the sides (9/2)^2
    [4-(9/2)]^2 = [5-(9/2)]^2 (let 4=a,9/2=b)
    4-(9/2) = 5-(9/2)
    4 = 5
    2+2 = 5

    And

    10x^2-19x=-6 =?


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    #10
    2cool4school
    Closed Accounts Posts: 162 ✭✭2cool4school


    youve lost me lads


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    #11
    stimpson
    Registered Users Posts: 7,815 ✭✭✭stimpson


    http://lmgtfy.com/?q=30%C3%B72(2%2B3)%C3%B75


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    #12
    desertstorm
    Registered Users Posts: 373 ✭✭desertstorm


    1290616506315.jpg


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    #13
    MoodeRator
    Registered Users Posts: 1,688 ✭✭✭MoodeRator


    nyarlothothep wrote: »
    What is 30÷2(2+3)÷5

    Is it 15?

    or 0.6?
    ...
    Or is this question broken?
    30÷2(2+3)÷5
    15(5)/5
    =15:confused:
    Maybe or maybe not. But I read it exactly the same as Papa smut


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    #14
    coffee_cake
    Moderators, Category Moderators, Politics Moderators, Recreation & Hobbies Moderators, Society & Culture Moderators Posts: 81,310 CMod ✭✭✭✭coffee_cake


    0.6 - brackets first, then multiplication, then divide left->right

    A common technique for remembering the order of operations is the abbreviation "PEMDAS", which is turned into the phrase "Please Excuse My Dear Aunt Sally". It stands for "Parentheses, Exponents, Multiplication and Division, and Addition and Subtraction".
    http://www.purplemath.com/modules/orderops.htm


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    #15
    MoodeRator
    Registered Users Posts: 1,688 ✭✭✭MoodeRator


    bluewolf wrote: »
    0.6 - brackets first, then multiplication, then divide left->right



    http://www.purplemath.com/modules/orderops.htm

    :o I'll just put my hat back on and go stand in my corner again.


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    #16
    Cool Mo D
    Registered Users Posts: 1,419 ✭✭✭Cool Mo D


    It's only a riddle if you can't remember primary school maths. Brackets first, then multiplication, then division. There is more than one division, then go left to right, giving 0.6.


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    #17
    MJRS
    Registered Users Posts: 331 ✭✭MJRS


    I thought multiplication and division were equal priority so you just do left to right? Hence the acronym being BOMDAS or BODMAS, both are valid. Isn't this one of loads of maths problems with two provable correct answers?

    Got this from the ever reliable wiki "These mnemonics may be misleading,
    especially if the user is not aware that
    multiplication and division are of equal
    precedence, as are addition and subtraction."


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    #18
    Saila
    Closed Accounts Posts: 7,751 ✭✭✭Saila


    answer = 0.6


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    #19
    onlyrocknroll
    Registered Users Posts: 750 ✭✭✭onlyrocknroll


    0.6

    Didn't your teacher teach you about BOMDAS?

    edit; oops missed MJRS's post


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    #20
    MARTINOZ
    Registered Users Posts: 24 ✭MARTINOZ


    Anyone that got 0.6 needs to go back to primary school.

    http://www.google.com.au/search?hl=en&source=hp&biw=1004&bih=610&q=30%2F2%282%2B3%29%2F5+%3D&oq=30%2F2%282%2B3%29%2F5+%3D&aq=f&aqi=&aql=f&gs_sm=e&gs_upl=1391l34015l0l17l17l2l6l0l0l453l2328l2-6.0.2


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    #21
    randombar
    Registered Users Posts: 3,360 ✭✭✭randombar


    Back in my day it was BOMDAS!!


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    #22
    davetherave
    Registered Users Posts: 3,359 ✭✭✭davetherave


    2cool4school wrote: »
    youve lost me lads

    Maybe you should have stayed in school?? :o ....sorry

    It's 0.6.

    30÷2(2+3)÷5 brackets first
    30÷2(5)÷5 then multiplication
    30÷10÷5 then division left to right
    3÷5
    0.6


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    #23
    28064212
    Registered Users Posts: 10,458 ✭✭✭✭28064212


    It's 15. The only way it could be 0.6 is if you redefine 5(2+3) to mean (5 * (2+3)) instead of 5 * (2+3). Bracket notation for multiplication is just shorthand, it doesn't change the precedence.

    30÷2(2+3)÷5
    = 30÷2(5)÷5
    = 30÷2*5÷5 (÷ and * have equal precedence and are left-associative, so you do them left-to-right)
    = 15*5÷5
    = 75÷5
    = 15

    The bolded part is where most people make their mistake. "Brackets first" means you calculate what is inside the brackets first. when brackets are used for multiplication it is just shorthand for *.

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    #24
    onlyrocknroll
    Registered Users Posts: 750 ✭✭✭onlyrocknroll


    28064212 wrote: »
    It's 15. The only way it could be 0.6 is if you redefine 5(2+3) to mean (5 * (2+3)) instead of 5 * (2+3). Bracket notation for multiplication is just shorthand, it doesn't change the precedence.

    30÷2(2+3)÷5
    = 30÷2(5)÷5
    = 30÷2*5÷5 (÷ and * have equal precedence and are left-associative, so you do them left-to-right)
    = 15*5÷5
    = 75÷5
    = 15

    The bolded part is where most people make their mistake. "Brackets first" means you calculate what is inside the brackets first. when brackets are used for multiplication it is just shorthand for *.

    Damn you, I thought I was right and now I'm confused.

    Why have you forsaken me BOMDAS? :(


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    #25
    im invisible
    Closed Accounts Posts: 4,373 ✭✭✭im invisible


    i dont know, maybe ask in the maths forum?:confused:


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    #26
    Mellor
    Registered Users Posts: 39,022 ✭✭✭✭Mellor


    JBnaglfar wrote: »
    ^^ I got that at first.

    If you want to get 15 you can.

    2(2+3) divided by 5 = 2
    30 divided by 2 = 15.

    This is basically asking 30 divided by 10 divided by 5, and I didn't think maths necessarily went from left to right.

    Edit: google suggests .6 is correct
    link
    no it doesn't

    http://www.google.ie/search?rlz=1C1DVCP_enIE394IE394&sourceid=chrome&ie=UTF-8&q=30+divided+by+10+divided+by+5#sclient=psy&hl=en&rlz=1C1DVCP_enIE394IE394&source=hp&q=30%C3%B72(2%2B3)%C3%B75&aq=&aqi=&aql=&oq=&pbx=1&bav=on.2,or.r_gc.r_pw.&fp=9838aa61b26af9a1&biw=1312&bih=560
    Cool Mo D wrote: »
    It's only a riddle if you can't remember primary school maths. Brackets first, then multiplication, then division. There is more than one division, then go left to right, giving 0.6.
    davetherave wrote: »
    Maybe you should have stayed in school?? :o ....sorry
    It's 0.6.

    30÷2(2+3)÷5 brackets first
    30÷2(5)÷5 then multiplication
    30÷10÷5 then division left to right
    3÷5
    0.6

    LMFAO

    Trying to be condesending and end up looking like a fool
    You should probably go back to school your self guys

    30÷2(2+3)÷5............so brackets first
    30÷2(5)÷5................2(5) is a shorthand way of writing 2x5, so lets change that so you don't get confused
    30÷2x5÷5..................Multiplication and division arecomplimentary so the order doesn't matter

    30x5÷5÷2
    30÷5÷2x5 etc all equal 15


    Anybody that is getting .6 is obviously dividing 30 by 10
    That's the same as dividing by both 2 and 5. Which is obviously wrong as their is no ÷ before the 5.
    For that to be the case it would have to read

    30÷(2(2+3))÷5 or 30÷2÷(2+3)÷5


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    #27
    martineatworld
    Registered Users Posts: 1,139 ✭✭✭martineatworld


    I don't know why anyone is being condescending tbh.

    According to Mellor's link, Google is putting in an extra pair of brackets to come up with that answer. There's an ambiguity about the structure of the question that leads me to believe that both answers are valid

    Which leads to petty squabbles on the internet about who's right given there are two valid ways.


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    #28
    28064212
    Registered Users Posts: 10,458 ✭✭✭✭28064212


    martineatworld wrote: »
    I don't know why anyone is being condescending tbh.

    According to Mellor's link, Google is putting in an extra pair of brackets to come up with that answer. There's an ambiguity about the structure of the question that leads me to believe that both answers are valid

    Which leads to petty squabbles on the internet about who's right given there are two valid ways.
    Google puts in brackets for clarification, it doesn't change the precedence. Put in 6 - 2 * 3 and it will "change" it to 6 - (2 * 3).

    The only way there's ambiguity is if you change 2(5) to mean something different to 2 * 5

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    #29
    Mellor
    Registered Users Posts: 39,022 ✭✭✭✭Mellor


    There is only something ambiguous if you make a mistake


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    #30
    ClutchIt
    Registered Users Posts: 709 ✭✭✭ClutchIt


    The question is broken really. Even though there is a correct way of doing it, anyone who writes an equation in that fashion is an ignoramus


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    #31
    GT_TDI_150
    Registered Users Posts: 10,917 ✭✭✭✭GT_TDI_150


    nyarlothothep wrote: »
    What is 30÷2(2+3)÷5

    Is it 15?

    or 0.6?
    ...
    Or is this question broken?

    just saw this,

    I thought you first caclulate whats in the brackets -> (2+3) = 5
    then you multiply it by 2 -> 2(5)=10
    then the 2 divisions are dont in the order they appear sp first 30/10=3
    then 3/5=.6

    could be well wrong


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