# Math, science

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assume the substance has a half-life of 12 years and the initial
amount is 133 grams. How long will it be until only 40 % remains?

• Math, science -

1(1/2)^(t/12) = .4
2^(-t/12) = .4
take log of both sides
(-t/12) log 2= log .4
t = -12 log .4/log2 = appr. 15.9 years.

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