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Math Help - too hard for this old guy

  1. #1
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    Question too hard for this old guy

    Using only numbers 1,2,7 & 8, each can be used only once, arrive at the number 37 by using plus, minus, multiplication or division in any order.
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  2. #2
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    How sure are you that it actually can be done?
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  3. #3
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    Wilmer

    The question was asked of me by my 11 yo grand daughter who got the question in her school homework. Glad I am not going to school now.
    Wilmer, thank you for your question.
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  4. #4
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    Quote Originally Posted by kennyk38 View Post
    Using only numbers 1,2,7 & 8, each can be used only once, arrive at the number 37 by using plus, minus, multiplication or division in any order.
    One way:
    concatenate the numbers
    { \dfrac{8}{2}-1} & 7 = 3&7 = 37

    .
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  5. #5
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    But that assumes brackets and indirect multiplication by 10
    (or division by .1) are allowed.

    Other ways are possible if not only +-/* are allowed, like:
    FLOOR(2^8 / 7 +1) or CEILING(2^8 / 7 * 1).

    Since this is a problem given to an 11 y.o. grand daughter
    (I have one of those too, Kenny; turned 11 last month!),
    I doubt that anything "complicated" is involved.

    I have a feeling that with only +-/* allowed, one of the
    4 numbers is a typo; if 1,2,7,9 : 29 + 1 + 7 = 37.
    Or if 1,2,7,8 to get 36 (not 37): (8 - 2) * (7 - 1) = 36.
    But that assumes brackets allowed.

    In other words, I think problem as stated is not possible...
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  6. #6
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    Thumbs up Thanks

    Quote Originally Posted by aidan View Post
    One way:
    concatenate the numbers
    { \dfrac{8}{2}-1} & 7 = 3&7 = 37

    .
    Aiden, many thanks for your help. You would be correct with your solution which is much appreciated.

    Kenny
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  7. #7
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    Quote Originally Posted by Wilmer View Post
    But that assumes brackets and indirect multiplication by 10
    (or division by .1) are allowed.

    Other ways are possible if not only +-/* are allowed, like:
    FLOOR(2^8 / 7 +1) or CEILING(2^8 / 7 * 1).

    Since this is a problem given to an 11 y.o. grand daughter
    (I have one of those too, Kenny; turned 11 last month!),
    I doubt that anything "complicated" is involved.

    I have a feeling that with only +-/* allowed, one of the
    4 numbers is a typo; if 1,2,7,9 : 29 + 1 + 7 = 37.
    Or if 1,2,7,8 to get 36 (not 37): (8 - 2) * (7 - 1) = 36.
    But that assumes brackets allowed.

    In other words, I think problem as stated is not possible...
    Wilmer, I have a solution to the problem, 8 divided by 2 minus 1 =3 and then 37. Many thanks for your input.
    Kenny
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  8. #8
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    Is that OK ... just 3 and 7 makes 37?
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  9. #9
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    Sorry no

    8 divided by 2 =4 - 1 =3 then do the 37 bit.
    Cheers and thanks.
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  10. #10
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    That involves a multiplication by 10: 3*10+7 = 37.

    If that's allowed, then why not split the 8 in half vertically:
    that'll give you two 3's, and: 33 + 7 - 2 - 1 = 37
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