\[a^{3}b \cdot 25b = 25a^{3}b^{2};\ \]
\[a = \frac{1}{5};\ \ b = 5:\]
\[25 \cdot \left( \frac{1}{5} \right)^{3} \cdot 5^{2} = 25 \cdot \frac{1}{125} \cdot 25 = 5.\]