Answer
18 percent.
Work Step by Step
Use the ideal gas model. $$PV=nRT$$
The volume and the temperature of the gas stay constant.
We see that the amount of gas remaining is proportional to the absolute pressure.
$$\frac{RT}{V}=\frac{P}{n}$$
$$\frac{P_1}{n_1}=\frac{P_2}{n_2}$$
$$\frac{n_2}{n_1}=\frac{P_2}{P_1}=\frac{5atm+1atm}{32atm+1atm}=\frac{6}{33}$$
This is the fraction of the original gas that remains.
$$\frac{6}{33}\approx 18\%$$
