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Math Help - exponentail growth

  1. #1
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    Unhappy exponentail growth

    Given: There are 7 billion, that is, 7*109
    people on Earth. If a bird flu virus starts
    with one person and within 5 days two
    people are infected, then each of those two
    people in 5 days infects 2 people each,
    and so on, how many days before everyone
    on earth is infected?
    Hint: Geometric series and logarithms
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  2. #2
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    Essentially it is saying that every 5 days, the population that is infected will double. How long until it reaches 7,000,000,000.
    The equation is N(t) = N_0 e^(rt)., where N_0 is the initial population (1 in this case), r is the rate of which it expands, and t is the time. You want to find when this equals 7 billion, so enter 7 billion on the other side and then solve for the time t. e is a constant, about 2.71.
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  3. #3
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    oh im sry that 10^9 power
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  4. #4
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    I am kinda confused.. so what would t and r be? how do i get that? and N_0 would be sub. as 1 ?
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