#### Answer

$-\dfrac{3}{10}$

#### Work Step by Step

Using concepts of exponents and radicals, the given expression, $
-\sqrt{\dfrac{9}{100}}
,$ is equivalent to
\begin{array}{l}\require{cancel}
-\sqrt{\dfrac{9}{100}}
\\\\=
-\sqrt{\left( \dfrac{3}{10} \right)^2}
\\\\=
-\dfrac{3}{10}
.\end{array}