1. How long will it take 600 grams of Plutonium 239 (half life 24,400 years) to decay to 18.75 grams?

2. How many grams of iodine 131 (half life 8.07 days) would be left after 48.42 days if you start with 25 grams?

3. Approximately how many years must a sample of Americium 241 (half life 458 years) be stored before it decays to a safe level?