Problem 1- A sample initially contains 3.2 moles of a radioactive isotope. How much of the sample remains after three half-lives?
2- Plutonium-236 is an alpha emitter with a half-life of 2.86 years. How long will it take for the 1.35mg sample of Pu?236 to decay to 0.160mg?
Express your answers to two significant figures separated by comma.