Question

There's 100 pounds of a radioactive material whose half-life is 5,000 years. In 10,000 years, how much material is left?

Answer 1

25 pounds

Explanation:

We can do this problem in two steps.

We start with 100 pounds of a material. The half-life is 5,000, so in 5,000 years there is 1/2 of the material left, so 50 pounds.

Then we go another 5,000 years, so there is 1/2 of the material again. Since there was 50 pounds at the start of this term, we're left with 25 pounds.