Question

If a radioactive material has a half-life of 5 years, what fraction of the material is left after 15 years?

A) 1/2

B) 1/4

C) 1/8

D) 1/16

Answer 1

After 15 years, which is equivalent to three half-lives of a radioactive material with a half-life of 5 years, 1/8 of the original amount remains.

Step-by-step explanation:

If a radioactive material has a half-life of 5 years, then after 15 years, three half-lives would have passed. Following the rule that with each half-life, half of the remaining material decays, we can calculate the fraction of material left after each half-life. After one half-life (5 years), 1/2 of the original material remains; after two half-lives (10 years), 1/4 remains; and after three half-lives (15 years), 1/8 remains. Therefore, the correct answer is C) 1/8.