A radioisotope has a half-life of 7.5 hours. How many half lives have occured after 67.5 hours? a 7 half-lives b 8 half-lives c 9 half-lives d 10 half-lives
To determine the number of half-lives that have occurred after 67.5 hours, divide the total time by the half-life:
67.5 hours / 7.5 hours/half-life = 9 half-lives.
Therefore, the answer is option c) 9 half-lives.