Homework Answers
t1/2 = 1.27*10^9 y
K = 0.693/t/12
= 0.693/1.27*10^9 = 5.45*10^-10 y^-1
The ration of Ar-40 to K-40 is 4.2 to 1
Then the fraction of K-40 remains = 1/4.2+1 = 1/5.2 = 0.1923
ln[A]/[A0] = -Kt
ln0.1923 = -5.45*10^-10*t
-1.6489 = 5.45*10^-10 * t
t = 1.6489/5.45*10^-10 = 3.02*10^9 y >>>answer
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