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Math Help - related rate problem

  1. #1
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    related rate problem

    If a snowball melts so that its surface area decreases at a rate of 3 cm2/min, find the rate at which the diameter decreases when the diameter is 12 cm. (Give your answer correct to 4 decimal places.)
    \frac{ds}{dt}=-3

    d=12

    S=4π r^2

    relating diameter(x) to radius:
    2r=x, r=\frac{x}{2}

    \frac{ds}{dt}=2π x\frac{dx}{dt}

    -3=2π (12)\frac{dx}{dt}

    \frac{dx}{dt}=\frac{-3}{24pi}

    =-.039788
    to 4 decimal places, -.0398
    I got the .
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  2. #2
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    Quote Originally Posted by hazecraze View Post
    If a snowball melts so that its surface area decreases at a rate of 3 cm2/min, find the rate at which the diameter decreases when the diameter is 12 cm. (Give your answer correct to 4 decimal places.)
    \frac{ds}{dt}=-3

    d=12

    S=4π r^2

    relating diameter(x) to radius:
    2r=x, r=\frac{x}{2}

    \frac{ds}{dt}=2π x\frac{dx}{dt}

    -3=2π (12)\frac{dx}{dt}

    \frac{dx}{dt}=\frac{-3}{24pi}

    =-.039788
    to 4 decimal places, -.0398
    I got the .
    Did it a little differently, but I get the same solution.
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