You may have multiplied by $\displaystyle\frac{{4}}{{5}}\usepackage{cmbright}\Huge\$ instead of its reciprocal: $\displaystyle\frac{{20}}{{3}}\cdot\frac{{4}}{{5}}\usepackage{cmbright}\Huge\$ . To solve the problem, multiply the first number by the reciprocal of the second number: $\displaystyle{6}\frac{{2}}{{3}}\div\frac{{4}}{{5}}=\frac{{20}}{{3}}\cdot\frac{{5}}{{4}}\usepackage{cmbright}\Huge\$