Question 1001210
 Actinium-225 has a half-life of 10 days. Suppose we have an initial amount of 100 grams of actinium-225. How much would be present after 30 days 
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A(t) = Ao*(1/2)^(t/10)
A(10) = 100*(1/2)^(30/10)
A(10) = 100*(1/2)^3 = 12.5 grams
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Cheers,
Stan H.
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