1. The half life of polonium-210 is 138.4 days. How many milligrams of polonium-210 remain after 415.2 days if you start with 2.0 mg of the isotope?
2. Assuming a half-life of 1599 years, how many years will be needed for the decay of 15/16 of a given amount of radium-226?
3. The half-life of radon-222 is 3.824 days. After what time will one-fourth of a given amount of radon remain?
4. The half-life of cobalt-60 is 5.27 years. How many milligrams of cobalt-60 remain after 52.7 years if you start with 10.0 mg?
5. A sample contains 4.0 mg of uranium-238. After 4.46 x 10 9 years, the sample will contain 2.0 mg of uranium-238. What is the half-life of uranium-238?