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 find the number of half-lives that have occurred after 67.5 hours, we divide 67.5 by the half-life of 7.5 hours.
67.5 / 7.5 = 9
Therefore, 9 half-lives have occurred after 67.5 hours.
Answer: c. 9 half-lives