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Math Help - [SOLVED] Complex Proportions

  1. #1
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    [SOLVED] Complex Proportions

    M is jointly proportional to a, b, and c and inversely proportional to d. If a and d have the same value and if b and c are both 2, then M=128.
    Express the statement as a formula. Use the given information to find the constant of proportionality. k=?
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  2. #2
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    You must get the magic words in your head.

    Directly Proportional ==> kx

    Inversely Proportional ==> k/x

    That's about it.

    "M is jointly proportional to a, b, and c and inversely proportional to d."

    M = k(abc)/d

    Really, that's all there is to translating these. The rest is a substitution exercise.

    "a = d"

    M = k(abc)/a = k(bc)(a/a) = kbc

    "b and c are both 2"

    M = kbc = k(2)(2) = 4k

    "M = 128"

    M = 4k = 128

    You should be able to solve that for 'k'.
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