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Math Help - Fish population problem.

  1. #1
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    Fish population problem.

    A large pond is stocked with fish. The fish population P is modeled by the formula P = 3t + 10t + 120, where t is the number of days since the fish were first introduced into the pond. How many days will it take for the fish population to reach 500?
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  2. #2
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    fish

    Ok, so the population wanted is 500. We plug in and now we have:

    500
    = 3t + 10t + 120, solve for t

    I suggest bringing the 3t and then 120 to the left side with subtraction then squaring both sides as your first few steps to solving for t.
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  3. #3
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    Quote Originally Posted by tmac11522 View Post
    A large pond is stocked with fish. The fish population P is modeled by the formula P = 3t + 10t + 120, where t is the number of days since the fish were first introduced into the pond. How many days will it take for the fish population to reach 500?
    500 = 3t + 10\sqrt{t} + 120

    0 = 3t + 10\sqrt{t} - 380

    let u = \sqrt{t} ...

    0 = 3u^2 + 10u - 380

    u = \frac{-10 \pm \sqrt{100 - 4(3)(-380)}}{6}

    taking the positive solution ...

    u \approx 9.7107 ...

    t = u^2 \approx 94.3 days
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