A radioactive sample has a half-life of one hour. If we start with 1 g of it at noon, how much remains at 3 PM? It is 0.125 g.
Work Step by Step
After one half-life, at 1pm, we are down to one-half the original amount, or 0.5 g. After two half-lives, at 2pm, we are down to one-quarter the original amount, or 0.25 g. After three half-lives, at 3pm, we are down to one-eighth the original amount, or 0.125 g. This is discussed on page 625.