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Math Help - Help with combinations Etc.

  1. #1
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    Help with combinations Etc.

    Hi, I'm having some problems with a few questions. I'm not cheating because we are given the answers and the work is not for marks. Please see Attached document Numbers

    Section A: 5
    Section B: 6, 8,9

    Please help :/
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  2. #2
    Junior Member Mrdavid445's Avatar
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    Re: Help with combinations Etc.

    5 A) I'm not sure if I'm seeing correctly, but I think the top part of the summation is a 6? If so, it's just 2^2+2^3+2^4+2^5+2^6=124

    8 B) Use Binomial-theorem

    9 B) Let the first term be x and the common ratio be y:
    Second term= xy
    Third term= xy^2
    ...
    Fifth term=xy^4
    We know x=18, so 18(y^4)=32/9
    And you can use that to find y
    And we know 8th term is x(y^7), and knowing x and y, we can get an answer.
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