What is the half-life of a radioactive isotope if a 500.0 g sample decays to 62.5 g in 24.3 hours?
You start with 500.0g.
After the first half-life, you have 250.0g.
After the second, you have 125.0g.
After the third, you have 62.50g.
Therefore, it takes three half-lives to decay to 62.50g.
Therefore, the elapsed time must be triple the length of one half-life.