Answer
$\dfrac{a^2b^5 - 2ab^6 + 3}{a^5b^7}$
Work Step by Step
$\frac{1}{a^3b^2} - \frac{2}{a^4b} + \frac{3}{a^5b^7}$
$= \frac{1 \times a^2b^5}{a^3b^2 \times a^2b^5} - \frac{2 \times ab^6}{a^4b \times ab^6} + \frac{3}{a^5b^7}$
$= \frac{a^2b^5 - 2ab^6 + 3}{a^5b^7}$