1) Strontium-90 is a byproduct in nuclear reactors fueled by the radioisotope uranium-235. The half-life of strontium-90 is 28.8 yr. What percentage of a strontium-90 sample remains after 75.0 yr?
2) 131I has a half-life of 8.04 days. Assuming you start with a 1.53 mg sample of 131I, how many mg will remain after 13.0 days