Question

If a sample of radioactive material has only 12.5% of the original radioactive parent material, how many half-lives have passed?

a. 3
b. 5
c. 6.25
d. 12.5

Answer 1

The correct answer is A) 3.

We can set up the equation 0.5ˣ = 0.125 to solve this, since we want to know the number of consecutive halves that are taken to get 12.5% (12.5% = 12.5/100 = 0.125).

To solve this, use logarithms:

`\log_(0.5)0.125=x \\ \\3=x`