Question

The half-life for the radioactive decay of calcium-47 is 4.5 days. how many half-lives have elapsed after 27 days?

Answer 1

1 half-life      - 4.5 days
x half-lives   - 27 days

x=(1*27)/4.5=6
6 half-lives have elapsed after 27 days.

Answer 2

Answer: The number of half lives are 6

Explanation:

We are given:

Half life of a radioactive isotope = 4.5 days

Calculating the number of half lives after time has elapsed 27 days:

4.5 days have been elapsed time after 1 half life

So, 27 days must have been elapsed after = $\frac{1}{4.5}\times 27=6$ half lives

Hence, the number of half lives are 6