# The half-life of radon-222 is 3.8 days. How much of a 100 g sample is left after 15.2 days?

Jun 17, 2016

$\text{15.2 days}$ is 4 HALF LIVES. A bit over $6 \cdot g$ of ""^222Rn will remain.
If 4 half lives have elapsed, $\frac{1}{2} \times \frac{1}{2} \times \frac{1}{2} \times \frac{1}{2}$ $=$ $\frac{1}{16}$ of the original quantity of ""^222Rn will remain.
Thus $100 \cdot g \times \frac{1}{16}$ $=$ ??*g