If a radioactive isotope has a half-life of 20 hours, how many half-lives have occured after 80 hours have passed?
a
3
b
5
c
4
d
2
The number of half-lives that have passed can be determined by dividing the total elapsed time by the half-life of the substance.
Given:
Total elapsed time = 80 hours
Half-life = 20 hours
Number of half-lives = Total elapsed time / Half-life
= 80 hours / 20 hours per half-life
= 4 half-lives
So, after 80 hours, 4 half-lives have occurred.
The correct answer is:
c) 4