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Math Help - find the formula

  1. #1
    Junior Member
    Joined
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    71

    find the formula

    A population has size 8000 at time with in years. (a) If the population decreases by 100 people per year, find a formula for the population, at time
    (b) If the population decreases by 15% per year, find a formula for the population, at time

    (a) I think it is 8000(-1.0100)^x

    PLEASE HELP ME!!!!!!!!!!!
    Last edited by asweet1; September 17th 2008 at 08:00 PM.
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  2. #2
    Senior Member
    Joined
    Dec 2007
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    Melbourne
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    You can check that your formula is right by substituting some obvious values for x.
    So after 1 year the population should be 7900 as it has decreased by 100 people in that year. Your formula gives -8080.

    The right answer to a is 8000-100x,
    and b is 8000(1-\frac{15}{100})^x = 8000(0.85^x).

    I don't like just giving people answers but I don't really know a process to get these; I just know them. sorry.
    Last edited by badgerigar; September 17th 2008 at 08:30 PM. Reason: fixed latex error
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