# Krypton-79 mg has a half-life of 35 h. How many half-lives have passed after 105 h?

Jun 12, 2017

$3$ half-lives

#### Explanation:

This question is rather simple; we're given a half-life ($35$ $\text{h}$) and asked how many occur in a given time ($105$ $\text{h}$).

To solve this, divide the time interval by the half-life:

$\left(105 \cancel{\text{h"))/(35cancel("h}}\right) = 3$ $\text{half-lives}$

It makes sense, as there are three $35 \text{-}$ hour intervals within $105$ hours.