By the time you begin the experiment, 1.04 g of barium-122 will remain.
The first step is to determine the number of half-lives that have elapsed.
Number of half-lives = 10 min × (1 half-life/2 min) = 5 half-lives
For each half-life, you divide the total amount of the isotope by 2.
Amount remaining = original amount × 1/2^(number of half-lives)
Amount remaining = 33.4 g x
After 10 min, 1.04 g of barium-122 will remain.