Answer
$-\dfrac{5a}{13c}$
Work Step by Step
Cancelling the common factor between the numerator and the denominator, the given expression, $
\dfrac{-20ab}{52bc}
,$ simplifies to
\begin{array}{l}\require{cancel}
\dfrac{\cancel{4b}\cdot(-5a)}{\cancel{4b}\cdot13c}
\\\\=
\dfrac{-5a}{13c}
\\\\=
-\dfrac{5a}{13c}
\end{array}
