GMAT Quantitative Reasoning Practice Test 1

George can fill $\frac{\mathit{Q}}{3}$ cans of paint in one minute. There are $\mathit{R}$ cans in one gallon, so $\frac{\mathit{R}}{\left(\frac{\mathit{Q}}{3}\right)}=3\frac{\mathit{R}}{\mathit{Q}}$ is the time it takes George to fill one gallon (in minutes). In 45 minutes George can fill up $\frac{45}{\left(3\frac{\mathit{R}}{\mathit{Q}}\right)}=15\frac{\mathit{Q}}{\mathit{R}}$.