Упростите выражение a^2/2b^2:(5/2ab*a^3/b).

\[\frac{a^{2}}{2b^{2}}\ :\left( \frac{5}{2ab} \cdot \frac{a^{3}}{b} \right) = \frac{a^{2}}{2b^{2}} \cdot \frac{b^{2} \cdot 2a}{5a^{3}} = \frac{1}{5}.\]