\[\left( \ \frac{25a^{2}}{8b^{2}} \right)^{3} \cdot \left( - \frac{16b^{4}}{125a^{3}} \right)^{2} =\]
\[= \left( \frac{5^{2}a^{2}}{2^{3}b^{2}} \right)^{3} \cdot \left( - \frac{2^{4}b^{4}}{5^{3}a^{3}} \right)^{2} =\]
\[= \frac{5^{6} \cdot a^{6} \cdot 2^{8} \cdot b^{8}}{2^{9}b^{6} \cdot 5^{6} \cdot a^{6}} = \frac{b^{2}}{2}\]