Question

Manganese-52 has a half-life of 6 days. How many days would a scientist have to wait for the radioactivity to be 12.5% the starting amount?

6
12
18
24

Answer 1

12.5% = 1/8 = (1/2)^3, so it takes 3 half-lives. With a 6-day half-life: 3 × 6 = 18 days.