Chapter 5 - Section 5.2 - More Work with Exponents and Scientific Notation - Exercise Set - Page 268: 53

$\dfrac{25}{8x^{5}y^{4}}$

Using laws of exponents, the given expression simplifies to \begin{align*} & \dfrac{2^{-3}x^2y^{-5}}{5^{-2}x^7y^{-1}} \\\\&= \dfrac{5^{2}x^{2-7}y^{-5-(-1)}}{2^{3}} \\\\&= \dfrac{25x^{-5}y^{-4}}{8} \\\\&= \dfrac{25}{8x^{5}y^{4}} .\end{align*}