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Math Help - Related Rates?

  1. #1
    Junior Member
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    Related Rates?

    If a population after t year is t^3+3t+90. Find the growth rate when t=4.

    t(4) =166

    3t^2 t' +3 t'

    t' (3t^2 +3) = 166

    t' = 166/ (3t^2 +3)

    t' = 166/(3(4)^2 +3)

    is this correct? I have no clue on how to do this problem at all...
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  2. #2
    Master Of Puppets
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    Re: Related Rates?

    The growth rate will be (t^3+3t+90)' = 3t^2+3.

    Now substitute t=4 giving 3(4)^2+3 = 51, you haven't given the units, so this could be thousands of people?
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