10th

what rate willl an amount double itself in 20 years at simple interest?

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  1. (1.00+x)^20 = 2 where x is the percent. If we call 1.00 + x = Y, then
    (Y)^20 = 2
    20*log(Y) = log 2
    20*log(Y) = 0.30103
    log Y = 0.30103/2 =
    Solve for y and that will tell you what 1+interest rate must be. Subtracting 1.00 will give you the interest rate. I get something like 3.5%

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  2. In 20 years you must make one times the original amount in interest.
    20 x = 1
    x = .05 or 5%

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  3. It said simple, not compound.

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  4. oops. You're right. I did compound.

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