Half-life of a radioactive element
If the half-life of a radioactive element is 30.0 years, how long will it take for a sample to decay to the point where its activity is 70.0% of the original value?
a. 15.4 years
b. 86.1 years
c. 5.0 years
d. 30.8 years
e. 12.2 years
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