<PRE><B>Question 323985</B>
Suppose that you have 12 grams of a substance, which decays exponentially and has a half-life of 23 years. How long will it be before there is only 1.5 grams left?
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A(t) = Ao*(1/2)^(t/23)
1.5 = 12*(1/2)^(t/23)
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(1/2)^(t/23) = 0.125
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Take the log of both sides:
(t/23)*log(1/2) = log(0.125)
t/23 = 3
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t = 69 years
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Cheers,
Stan H.</PRE>