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Math Help - Inversely proportional

  1. #1
    Senior Member Mukilab's Avatar
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    Inversely proportional

    Have I done this correctly?

    f is inversely proportional to d

    when d=50, f=256
    Find value of f when d=80

    Figured out a constant of 25/125

    so

    f=50/1*125/25=250

    Is thsi correct?
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  2. #2
    Senior Member nikhil's Avatar
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    Lightbulb

    its incorrect
    since f is inversely proportional to d we have
    f=k/d where k is a constant
    now as f=256 when d=50 then
    k=fd=50*256
    so value of f when d=80
    f=(50*256)/80=160
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  3. #3
    MHF Contributor
    skeeter's Avatar
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    f is inversely proportional to d ...

    f = \frac{k}{d}

    ... where k is the constant of proportionality.


    substitute in the given values to solve for k ...

    256 = \frac{k}{50}

    k = 50 \cdot 256 = 12800<br />

    f = \frac{12800}{d}

    ... finish the problem
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  4. #4
    Senior Member Mukilab's Avatar
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    ah I did d/k.

    Thanks.
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