Question

The half life of `"^131I` is 8.021 days. What fraction of a sample of `"^131I` remains after 24.063 days?

Answer 1

After three half-lines (`{24}/8=3`) one eighth of the original iodine-131 (`1/2 × 1/2 × 1/2`) remains.

Explanation:

Start with your sample of iodine-131. In one half-life, just over eight days, half of the sample decays leaving the other half. That remaining half is in effect its own sample in which half decays again after another half-life. You're now left with one-fourth of the original iodine-131 with half decaying in the third half-life from when you started.