Question

Strontium-90 is a radioactive waste product from nuclear reactors. It has a half-life of 29 years. How many years will it take for a quantity of strontium-90 to decay to 1/16 (one-sixteenth) of its original mass?

Answer 1

since 1/16 = (1/2)^4
It will take 4 half-lives to decay that far.