Question

A sample of U-235 has a half-life of 700 million years. What fraction of the parent material will remain after 2800 million years?

a. 1/2
b. 1/4
c. 1/8
d. 1/16
e. 1/32

Answer 1

After 2800 million years, the fraction of the parent material that will remain is 1/16.

Step-by-step explanation:

To find the fraction of the parent material that will remain after 2800 million years, we need to determine how many half-lives have passed. Since the half-life of U-235 is 700 million years, dividing 2800 million years by 700 million years gives us 4 half-lives. In each half-life, half of the parent material decays. Therefore, after 4 half-lives, the fraction of the parent material that will remain is (1/2)^(4) = 1/16.