Let $\displaystyle{t}=\usepackage{cmbright}\Huge\$ the time, in hours, it takes the repairman to fix one pair of shoes. Then $\displaystyle{2}{t}=\usepackage{cmbright}\Huge\$ the amount of time it takes the assistant. Their rates are $\displaystyle\frac{{1}}{{t}}\usepackage{cmbright}\Huge\$ and $\displaystyle\frac{{1}}{{{2}{t}}}\usepackage{cmbright}\Huge\$ pairs per hour. You may have added these fractions incorrectly when finding their combined rate. To add two fractions, you must rewrite one or both so that they have a common denominator.