Question

LQQ#2 Sodium-24 has a half-life of 15 hours. How

many grams of a 450 g sample will remain after 45
hours?

Answer 1

Notice that 45 hours is 3 times the half-life of 15 hours.

After the first 15 hours, 450 g decays to half this amount, 225 g.

After the next 15 (total 30), 225 g decays to 112.5 g.

After the next 15 (total 45), 112.5 g decays to 56.25 g.