# Gold-198 has a half-life of 2.7 days. How much of a 96g sample of gold-198 will be left after 8.1 days?

Since $8.1 = 3 \times 2.7$ there will be three halvings:
$\frac{1}{2} \times \frac{1}{2} \times \frac{1}{2} = \frac{1}{8}$th will be left. This is $\frac{1}{8} \times 96 = 12 g$