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Math Help - Which equation would I use?

  1. #1
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    Which equation would I use?

    I have some math problems that I'm confused on...

    I was given these formulas to work with:

    A(t) = A_{0}(1+r)^t
    A(t) = A_{0}b^{tk}
    P(t) = P_{0}e^{rt}
    A(t) = A_{0}(1\\\pm r/k)^{t*k}

    If 500 fleas triple in their population every 18 hours:
    1) How many fleas will there be in 3 days?
    I got 40500, but will someone confirm whether this is right?

    2) How long will it take for there to be 1200 fleas?
    I got 14.34 hours, but again, I'm not too confident in my solution. Could someone possibly confirm this as well?
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  2. #2
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    Quote Originally Posted by sregg43 View Post
    I have some math problems that I'm confused on...

    I was given these formulas to work with:

    ...
    A(t) = A_{0}b^{tk} <<<< this one is sufficient for your problems
    ...

    If 500 fleas triple in their population every 18 hours:
    1) How many fleas will there be in 3 days?
    I got 40500, but will someone confirm whether this is right? <<<< correct!

    2) How long will it take for there to be 1200 fleas?
    I got 14.34 hours, but again, I'm not too confident in my solution. Could someone possibly confirm this as well?
    1. I assume that you use the general equation

    A(t)=500 \cdot 3^{k \cdot t}

    with k = \frac1{18} and t measured in hours.

    2. You have to solve for t:

    1200 = 500 \cdot 3^{\frac1{18} \cdot t}

    \frac{12}{5} =  3^{\frac1{18} \cdot t}

    Now use logarithms. BTW I've got the same result.
    Last edited by earboth; February 8th 2010 at 12:27 AM. Reason: typo
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