$\displaystyle{20}={2}\cdot{2}\cdot{5}\usepackage{cmbright}\Huge\$ and $\displaystyle{52}={2}\cdot{2}\cdot{13}\usepackage{cmbright}\Huge\$ .

The least common multiple is $\displaystyle{2}\cdot{2}\cdot{5}\cdot{13}={260}\usepackage{cmbright}\Huge\$ .