Chapter R - Elementary Algebra Review - R.1 Introduction to Algebraic Expressions - R.1 Exercise Set - Page 938: 21

$-\dfrac{1}{2}$

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}