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

1 Answer
May 22, 2017


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


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.