Work Step by Step
After each half-life, one-half of the remaining material decays. After one half-life, one day, we are down to one-half the original amount. After two half-lives, 2 days, we are down to one-quarter the original amount. After three half-lives, 3 days, we are down to one-eighth the original amount. This means that 7/8 of the original sample has decayed.