<PRE><B>Question 694065</B>
Half life of a radioactive substance is 33.6 years
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1/2Ao = Ao(1/2)^(t/33.6)
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a) find rate of decay
rate = 1 - (1/2)^(1/33.6) = 1-0.9796 = -0.0204
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b) how much of the sample of 400 grams will remain after 20 years?
x = 400(1/2)^(20/33.6)
x = 254.77 grams
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c)how long will it take a sample of 400 grams to decay to 300?
300 = 400(1/2)^(t/33.6)
(1/2)^(t/33.6) = 0.75
(t/33.6)log(0.5) = log(0.75)
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t/33.6 = 0.4150
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t = 13.95 years
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Cheers,
Stan H.
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