You probably followed the incorrect order of operations. This would have been the answer if the problem were to simplify $\displaystyle{{\left(\frac{{{x}}^{{5}}}{{{x}}^{{10}}}\right)}}^{{4}}\usepackage{cmbright}\Huge\$ . To follow the correct order of operations, you must simplify the numerator first. To do this you need to use the power rule: $\displaystyle{{\left({{x}}^{{a}}\right)}}^{{b}}={{x}}^{{{a}\cdot{b}}}\usepackage{cmbright}\Huge\$ . Then use the quotient rule.