Question

If you have 40 milligrams of uranium-232 that has a half-life of 70 years, how much of uranium-232 will remain in 140 years?

a. 10 mg
b. 20 mg
c. 5 mg
d. 2.5 mg

Answer 1

The amount of uranium-232 that will remain in 140 years is A)10 mg.

Step-by-step explanation:

To determine the amount of uranium-232 that will remain in 140 years, we need to calculate the number of half-lives that have elapsed. Each half-life is 70 years, so dividing 140 by 70 gives us 2 half-lives.

Each half-life reduces the amount of uranium-232 by half. So to find the amount remaining after 2 half-lives, we multiply the initial amount (40 mg) by 0.5 twice, because (0.5)*(0.5) = 0.25.

Therefore, the amount of uranium-232 that will remain in 140 years is 40 mg * 0.25 = 10 mg (option a).