[tex] \frac{625 {(5xy)}^{ - 3} }{ {(5x)}^{2} {y}^{7} } \: = \: 625 \times \frac{1}{ {(5xy)}^{3} } \times \frac{1}{ {(5x)}^{2} {y}^{7} } \: = \: 625 \times \frac{1}{125 {x}^{3} {y}^{3} } \times \frac{1}{25 {x}^{2} {y}^{7} } \: = \: \frac{1}{5 {x}^{5} {y}^{10} } [/tex]
