You may have thought that the probability would be $\displaystyle\frac{{1}}{{4}}\usepackage{cmbright}\Huge\$ because there are four sections. This would be the case if the sections were equal in size, but they are not. The probability of pointing to green is less than $\displaystyle\frac{{1}}{{4}}\usepackage{cmbright}\Huge\$ because green takes up less than $\displaystyle\frac{{1}}{{4}}\usepackage{cmbright}\Huge\$ of the circle.