If you know an isotope has a half life of 47 days, which of the following best represent how long has the sample been decaying if approximately 10% of the original radioactive isotope is left?

Question

Quizplus · Accepted Answer

The sample has gone through approximately 3.32 half-lives to reach 10% of its original amount (since (1/2)^3.32 ≈ 0.10). Multiplying 3.32 by the half-life of 47 days gives approximately 156 days, which is closest to 150 days.

If You Know an Isotope Has a Half Life of 47