The half-life of carbon-11 is 20 min. a sample of carbon-11 has 25 mci. how many half-lives of carbon-11 occur in 1 hour? how much carbon-11 is in the sample 1 hour after the original sample is measured? a. 3 half-lives; 0.313 mci b. 4 half-lives; 1.563 mci c. 3 half-lives; 3.125 mci d. 4 half-lives; 23 mci