1. **State the problem:** Simplify the expression $\frac{y-x}{x^2 y^3}$. 2. **Recall the formula and rules:** When simplifying algebraic fractions, divide each term in the numerator by the denominator separately if possible, and apply the laws of exponents: $\frac{a^m}{a^n} = a^{m-n}$. 3. **Rewrite the expression:** $$\frac{y-x}{x^2 y^3} = \frac{y}{x^2 y^3} - \frac{x}{x^2 y^3}$$ 4. **Simplify each term:** $$\frac{y}{x^2 y^3} = \frac{y^{1}}{x^{2} y^{3}} = x^{-2} y^{1-3} = x^{-2} y^{-2}$$ $$\frac{x}{x^2 y^3} = \frac{x^{1}}{x^{2} y^{3}} = x^{1-2} y^{-3} = x^{-1} y^{-3}$$ 5. **Combine the simplified terms:** $$x^{-2} y^{-2} - x^{-1} y^{-3}$$ 6. **Express with positive exponents if preferred:** $$\frac{1}{x^{2} y^{2}} - \frac{1}{x y^{3}}$$ **Final answer:** $$x^{-2} y^{-2} - x^{-1} y^{-3}$$