Assignment 16776

27 years. How many milligrams of cobalt-60 remain after 52.7 years if you start with 15 mg?
A sample contains 12.0 mg of an unknown element. After 4.46 × 109
years, the sample will contain 3.00 mg of the unknown element. What is
the half-life of the unknown element?
Please show the work for each question.