A radioisotope has a half life of 7.5 hours. How many half lives have occurred after 67.5 hours?
To find out how many half-lives have occurred after 67.5 hours, we divide the total time by the half-life.
67.5 hours divided by 7.5 hours = 9 half-lives.
Therefore, after 67.5 hours, 9 half-lives have occurred.