\[\frac{5^{n + 1} - 5^{n - 1}}{2 \cdot 5^{n}} = \frac{5^{n}\left( 5 - 5^{- 1} \right)}{2 \cdot 5^{n}} =\]
\[= \frac{5 - \frac{1}{5}}{2} = \frac{5 - 0,2}{2} = \frac{4,8}{2} = 2,4.\]