Assume you are observing 600 atoms of U-238. U-238 decays into Pb-206 and has a half-life of 4.5 billion years. use this information to answer the following questions.
1) what percentage of the original U-238 remains after 9 billion years has passed?
2) How many half-lives have passed if you now have a sample with 300 atoms of U-238?
3) How much time has passed if you have a sample of 525 atoms of Pb-206?