Question

Indium-117 has a half-life of 43 minutes. If you start with 500 grams of indium-117, how much time will it take to have 31.25 grams of indium-117 left in the sample?​

Answer 1

500 / 31.25 = 16

(1/2)^n = 1/16 where n is the number of elapsed half-lives

(1/2)^4 = 1/16 so the sample has gone thru 4 half-lives

43 min * 4 = 172 min = 2.87 hrs