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

This can be solved by the equation:

A = Aoe^ (-ln2/t) T

where Ao is the initial amount of the substance (73.9-g sample of radon-222), t is the half-life time (3.8 days) and T is the time elapsed. Plugging in the values in the equation, the substance left is 1.11g.