Radioactive decay: A radioactive sample has a half-life of 10 min. What fraction of the sample is left after 40 min?

Question

Quizplus · Accepted Answer

Since the half-life is 10 min, after the first 10 min, only 1/2 of the original sample is left. After the next 10 min (20 min total), only 1/2 of that remaining sample is left, which is 1/2 * 1/2 = 1/4 of the original sample. After 30 min, only 1/2 of that remaining sample is left, which is 1/2 * 1/4 = 1/8 of the original sample. After 40 min, only 1/2 of that remaining sample is left, which is 1/2 * 1/8 = 1/16 of the original sample. Therefore, the fraction of the sample left after 40 min is 1/16. So, the answer is D.

Radioactive Decay: a Radioactive Sample Has a Half-Life of 10