You may have divided the first fraction on the top by the first fraction on the bottom, and then divided the second fraction on the top by the second fraction on the bottom, and added the results. This is the incorrect order of operations. First simplify the numerator to $\displaystyle\frac{{4}}{{10}}\usepackage{cmbright}\Huge\$ and the denominator to $\displaystyle\frac{{3}}{{5}}\usepackage{cmbright}\Huge\$ . Then divide: $\displaystyle\frac{{4}}{{10}}\div\frac{{3}}{{5}}\usepackage{cmbright}\Huge\$