An isotope of radon gas, Rn-222, undergoes decay with a half-life of 3.8 days. How long does it take for the amount of Rn-222 to be decreased to one-sixteenth of the original amount?

Answer 1

well, 1/16 = 1/2^4

so it takes 4 half-lives

Answer 2

Wrong, it takes 15.2 days