Half life help!

Question

Tritium is a radioactive form of hydrogen with a half- life of 12.3 years. If 48.0 mg is accidentally released from a nuclear power plant, how much will remain after 49.2 years? Round to the correct number of significant figures and use units (mg)

Answer 1

If the half life is 12.3 years and 49.2 years passed this is 4 half lives. Of the 48.0 mg we would have 3.0 mg left