# The radioisotope radon-222 has a half life of 3.8 days. How much of a 73.9 g sample of radon-222 would be left after approximately 23 days?

Use the 1st order decay equation C_("final") = C_"initial" e^(-kt)
=> ${C}_{\text{final}}$ = 1.11 grams Rn-222 after 23 days.