The commutative property of addition states that $\displaystyle{a}+{b}={b}+{a}\usepackage{cmbright}\Huge\$ . Therefore, you may switch the order of $\displaystyle\frac{{2}}{{3}}\usepackage{cmbright}\Huge\$ and $\displaystyle\frac{{1}}{{5}}\usepackage{cmbright}\Huge\$ .