Question

The half-life of a radioactive isotope is the time it takes for a quantity of the isotope to be reduced to half its initial mass. Starting with 150 grams of a radioactive isotope, how much will be left after 3 half-lives?

Answer 1

After 3 half-lives, the remaining amouunt will reduced by a factor of (2*2*2) or 8.

So 150 grams after 3 half-lives will be reduced to 150 / 8 = 18.75 grams.