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Math Help - what number should be written in the brackets

  1. #1
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    what number should be written in the brackets

    hello all , Can u please help me understand why c) 672 is thr right answear in this one :

    156(108)138
    260( ? )148


    a)135 , b)448 , c)672 , d)158 , e )240
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  2. #2
    Junior Member guildmage's Avatar
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    Are you sure that's how it's written? Are there no other information regarding that question?
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  3. #3
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    hiya , yea thats exactly how its written and thats everything , supposed to find the logic in the numbers but i cant
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  4. #4
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    Hello, edendeli!

    If that's all that is given, there is no unique answer.



    Help me understand why (c)\;672 is the right answer:

    . . \begin{array}{c}156(108)138 \\ 260(\;\;?\;\;)148 \end{array}

    . . (a)\;135 \qquad (b)\;448 \qquad (c)\;672 \qquad (d)\;158 \qquad (e)\;240

    It doesn't help to say "That's exactly how it's written."
    There must be some other clues somewhere . . .


    Are those 9-digit numbers? . \begin{array}{c}156108138 \\ 260abc148 \end{array}


    Are they sets of 3-digit numbers? . \begin{array}{c}<br />
156,\;(108),\;138 \\ 260,\;(abc),\;(148) \end{array}


    We can only guess at the intent of the problem.


    Here's one guess . . .

    Suppose the middle number is a function of the other two numbers.

    . . That is: . \begin{Bmatrix}f(156,138) &=& 108 \\ f(260,148) &=& ?\end{Bmatrix} \quad\Rightarrow\quad z\:=\:f(x,y)

    Then there are several brizillion possible functions.



    Here's a function that produces answer (c)\;672

    . . . . . z \:=\:6(x-y)

    That is, subtract the two outer numbers, and multiply by 6.



    But this function produces answer (a)\;135

    . . z \;=\;\dfrac{441}{2132}x + \dfrac{45}{82}y



    And this function produces answer (e)\;240

    . . z \;=\;\dfrac{714}{533}x - \dfrac{30}{41}y



    Conclusion: The author took too much cough syrup . . .
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  5. #5
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    Thanks very much for your reply
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  6. #6
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    But thats exactly literally everything :
    25 .What number should be written in the brackets below :
    158(108)138
    260( ? )148

    ... and the possible answears below that ...


    " subtract the two outer numbers, and multiply by 6" - i think thats it
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  7. #7
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    Hello, eveyone!

    I still maintain that the problem is grotesquely silly . . .


    Quote Originally Posted by edendeli
    "Subtract the two outer numbers, and multiply by 6"
    i think thats it

    That's only because we were given the answer.
    . . By the way, how were you told that the answer is (c)?



    To make my point, I made up a similar problem
    . . without giving you the answer.


    Given: . f(1,2) \,=\,9

    Find: . f(3,7)

    . . (a)\;27 \qquad(b)\;28 \qquad (c)\;29 \qquad (d)\;30 \qquad (3)\;31


    ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~

    Spoiler:

    \text{If }f(x,y) \,=\,9x,\:\text{ then: }\:f(3,7) \:=\:9\!\cdot\!3 \:=\:27\;\text{ answer (a)}

    \text{If }f(x,y) \:=\:7x+y,\:\text{ then: }\:f(3,7) \:=\:7\!\cdot\!3 +7 \:=\:28\;\text{ answer (b)}

    \text{If }f(x,y) \:=\:5x+2y,\:\text{ then: }\:f(3,7) \:=\:5\!\cdot\!3 + 2\!\cdot\!7 \:=\: 29\;\text{ answer (c)}

    \text{If }f(x,y) \:=\:3(x+y),\:\text{ then: }\:f(3,7) \:=\:3(3+7) \:=\:30\;\text{ answer (d)}

    \text{If }f(x,y) \:=\:x+4y,\:\text{ then: }\:f(3,7) \:=\:3 + 4\!\cdot\!7 \:=\:31\;\text{ answer (e)}


    NOW do you believe me?

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  8. #8
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    Hello again ,
    I obviously havent made myself clear in my previous thread , first i meant thanks very much for taking your time replying to me , after that i just copied your suggested answear and just wrote that i think thats the right logic that they are looking for me to find ( the one you've given , not like i just found it myself ! ) and i yea i agree with you that is incredibly silly and makes no sense at all ,its from an expample test that includes 5 different moduls - maths , literature,history etc ,the maths one include 10 tasks with few " logical " problems , u only have a minute to asnwear each question as well , .... oh and i have the answeasr after each test so thats how i know its C the right answear !
    and again thanks for your help .......
    Last edited by edendeli; July 16th 2010 at 02:36 AM.
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