Answer
$-\dfrac{1}{2}$
Work Step by Step
Using operations on real numbers, the given expression, $
\left( -\dfrac{3}{10} \right)+\left( -\dfrac{1}{5} \right)
,$ evaluates to
\begin{array}{l}\require{cancel}
-\dfrac{3}{10}-\dfrac{1}{5}
\\\\=
-\dfrac{3}{10}-\dfrac{2}{10}
\\\\=
\dfrac{-3-2}{10}
\\\\=
\dfrac{-5}{10}
\\\\=
-\dfrac{\cancel{5}}{\cancel{5}\cdot2}
\\\\=
-\dfrac{1}{2}
.\end{array}