You may have switched the base, 120, and the amount, 48, and solved the equation $\displaystyle{n}\cdot{48}={120}\usepackage{cmbright}\Huge\$ . The correct equation to solve is $\displaystyle{n}\cdot{120}={48}\usepackage{cmbright}\Huge\$ . Also, you did not move the decimal point when converting to a percent.