Answer
Only 50.0 mg of fluorine-18 are still active after 110 min.
Work Step by Step
1. Calculate the number of half-lives.
$110 min \times \frac{1half-life}{110 min} = 1 half-life$
2. Now, calculate the remaining mass after 1 half-life:
1 Half Life: $100.mg \times \frac{1}{2} = 50.0 mg$
