math

An unknown radioactive element decays into non-radioactive substances. In 100 days the radioactivity of a sample decreases by 64 percent.
a)(a) What is the half-life of the element? half-life:
b)How long will it take for a sample of 100 mg to decay to 51 mg?
time needed:

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  1. .36 = (1/2)^(100/k)
    k = 67.84

    so, the half-life is 67.84 days
    Makes sense, since the sample has decreased by a little more than 1/2 in 100 days.

    51/100 = (1/2)^(t/67.84)
    t = 65.9 days

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