172. After 3 days a sample of radon-222 decayed to 58% of its original amount. (a) What is the half life of radon-222? (b) How long would it take the...

172. After 3 days a sample of radon-222 decayed to 58% of its original amount. (a) What is the half life of radon-222? (b) How long would it take the sample to decay to 10% of its original amount? 173. Polonium-210 has a half life of 140 days. (a) If a sample has a mass of 200 mg find a formula for the mass that remains after t days. (b) Find the mass after 100 days. (c) When will the mass be reduced to 10 mg?