Incorrect. The least common denominator is equal to the least common multiple of 4 and 10. Since $\displaystyle{4}={2}\cdot{2}\usepackage{cmbright}\Huge\$ and $\displaystyle{10}={2}\cdot{5}\usepackage{cmbright}\Huge\$ , this is $\displaystyle{2}\cdot{2}\cdot{5}={20}\usepackage{cmbright}\Huge\$ .