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

Answer 1

(1/2)^n = 1/16
n = 4 half lives

4 * 29 = 116 years

if you did not see that 2^4 = 16 then you could do
.5^n = .0625
n log .5 = log .0625
n = log .0625 / log .5