Question

The half-life of caffeine in a person’s bloodstream is about 6 hours. If a person’s bloodstream contains 80 milligrams of caffeine, how much of that caffeine will remain after 14 hours?

Answer 1

To calculate the remaining caffeine, we use the radioactive decay formula which is expressed as An = Aoe^-kt where An is the amount left after t time, Ao is the initial amount and k is a constant we can calculate from the half-life information. We do as follows:
at half-life,
ln 1/2 = -k(6)
k = 0.12/hr

An = 80e^-0.12(14)
An = 15.87 mg