10 (53) 57 (55) =

10. $$\frac{(5^3)^5 \cdot 5^7}{(5^5)^4} = \frac{5^{3\cdot5} \cdot 5^7}{5^{5\cdot4}} = \frac{5^{15} \cdot 5^7}{5^{20}} = \frac{5^{15+7}}{5^{20}} = \frac{5^{22}}{5^{20}} = 5^{22-20} = 5^2 = 25$$

Ответ: 25