Answer
$\dfrac{10a^2}{b^5}$
Work Step by Step
RECALL:
(i) $\dfrac{a^m}{a^n} = a^{m-n}, a \ne 0$
(ii) $a^{-m} = \dfrac{1}{a^m}, a\ne0$
Divide the coefficients by each other and the variables by each other to obtain:
$=\dfrac{20}{2} \cdot a^{3-1} \cdot b^{8-13}
=10 \cdot a^{2} \cdot b^{-5}$
Use rule (ii) above to obtain:
$=10a^2 \cdot \dfrac{1}{b^5}
\\=\dfrac{10a^2}{b^5}$
