Question

A 40.0 milligram sample of 33-P decays to 10.0 milligrams in 50.0 days. What is the half-life of 33-P?

Answer 1

10.0 mg / 40.0 mg = 1/4 left after 50 days

(1/2)^2 = 1/4 so 2 half-lives have occurred

2 half-lives = 50 da

half-life = 25 da