calculus

Suppose that the sales at Borders bookstores went from 68 million dollars in 1990 to 427 million dollars in 1995 . Find an exponential function to model the sales (in millions of dollars) as a function of years,t, since 1990.

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  1. t = 0 in 1990
    t = 5 in 1995

    s = A e^kt
    when t = 0, s = 68
    so
    68 = A

    when t = 5
    427 = 68 e^5k
    6.28 = e^5k
    ln 6.28 = 1.84 = 5 k
    so
    k = .367
    so
    s = 68 e^.367 t

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