Question

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

Answer 1

`3` half-lives

Explanation:

This question is rather simple; we're given a half-life (`35` `"h"`) and asked how many occur in a given time (`105` `"h"`).

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

`(105cancel("h"))/(35cancel("h")) = 3` `"half-lives"`

It makes sense, as there are three `35"-"` hour intervals within `105` hours.