Half-life of a drug in the bloodstream problem

Question

The​ half-life of a drug in the bloodstream is 18hours. What fraction of the original drug dose remains in 36 hours? in 60 hours?

Answer 1

After 18 hours, half is left

After a SECOND 18 hours (36 total), half of a half, or, one quarter is left.

To solve for 60 hours, which is not a multiple of 18, you need to use a formula:

A = Ao (2)^-t/h

t is the amount of time elapsed, h is the half life

A = Ao (2^-60/18)

A = Ao (2^-3.33)

A = Ao (.0994)

so, about 10 percent is left.