\[\sqrt{5}\left( \sqrt{10} + \sqrt{5} \right) - \frac{5}{2}\sqrt{8} =\]
\[= \sqrt{5 \cdot 10} + \sqrt{5 \cdot 5} - \frac{5}{2}\sqrt{4 \cdot 2} =\]
\[= 5\sqrt{2} + 5 - \frac{5}{2} \cdot 2\sqrt{2} =\]
\[= 5\sqrt{2} + 5 - 5\sqrt{2} = 5.\]