Question

Seven-eighths of a sample of hydrogen-3 will have become a stable isotope after 36.9 years. What is the half-life of hydrogen-3?

12.3 years
18.5 years
32.3 years
36.9 years

Answer 1

After 36.9 years only 1/8 of the sample remains, and 1/8 = (1/2)^3, so three half-lives have passed. Thus the half-life = 36.9 / 3 = 12.3 years.