The half-life for the radioactive decay of U-238is 4.5 billion years and is independent of initial concentration.A) How long will it take for 20% of the U-238 atoms in a sample of U-238 to decay?B) If a sample of U-238 initially contained 1.6×1018 atoms when the universe was formed 13.8 billion years ago how many U-238 atoms will it contain today?
