Answer
$\dfrac{10}{a^{6}b^{2}}$
Work Step by Step
Using the laws of exponents, the given expression, $
(5a^{-2}b^{-3})(2a^{-4}b)
$, is equivalent to
\begin{array}{l}
5(2)a^{-2+(-4)}b^{-3+1}
\\\\=
10a^{-6}b^{-2}
\\\\=
\dfrac{10}{a^{6}b^{2}}
.\end{array}