You may have multiplied 4 by the reciprocal of $\displaystyle{5}\frac{{7}}{{9}}\usepackage{cmbright}\Huge\$ , which is $\displaystyle\frac{{9}}{{52}}\usepackage{cmbright}\Huge\$ . You want to multiply $\displaystyle\frac{{52}}{{9}}\usepackage{cmbright}\Huge\$ by the reciprocal of $\displaystyle{4}\usepackage{cmbright}\Huge\$ , which is $\displaystyle\frac{{1}}{{4}}\usepackage{cmbright}\Huge\$ .