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?

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