How much of a radioactive kind of copper will be left after 39 hours if you start with 64 grams and the half-life is 13 hours?
39 hours is 3 half lives
64 * 1/2 * 1/2 * 1/2 = 69 * 1/8 = ....... grams left
The "9" in 69 * 1/8 is a typo. The guest actually meant 64 * 1/8.
64 grams with a half life of 13 hours
After the 1st 13 hours there's 32 grams left
After the 2nd 13 hours there's 16 grams left
After the 3rd 13 hours there's 8 grams left
