\[\frac{5 - \sqrt{5}}{\sqrt{10} - \sqrt{2}} = \frac{\sqrt{5}\left( \sqrt{5} - 1 \right)}{\sqrt{2}\left( \sqrt{5} - 1 \right)} =\]
\[= \frac{\sqrt{5}}{\sqrt{2}} = \sqrt{\frac{5}{2}} = \sqrt{2,5}.\]