One way to subtract is to regroup one of the whole numbers: $\displaystyle{3}\frac{{1}}{{4}}={2}+{1}+\frac{{1}}{{4}}={2}+\frac{{4}}{{4}}+\frac{{1}}{{4}}={2}\frac{{5}}{{4}}\usepackage{cmbright}\Huge\$ . Then subtract: $\displaystyle{2}\frac{{5}}{{4}}-{1}\frac{{3}}{{4}}={1}\frac{{2}}{{4}}={1}\frac{{1}}{{2}}\usepackage{cmbright}\Huge\$ .