Chapter 1 - Introduction to Algebraic Expressions - 1.7 Multiplication and Division of Real Numbers - 1.7 Exercise Set - Page 59: 124

$-\dfrac{1}{2}$

Using the $LCD= 10 $, the given expression, $ \dfrac{3}{-10}+\dfrac{-1}{5} $, simplifies to \begin{array}{l}\require{cancel} \dfrac{-1(3)+2(-1)}{10} \\\\= \dfrac{-3-2}{10} \\\\= \dfrac{-5}{10} \\\\= \dfrac{-1}{2} \\\\= -\dfrac{1}{2} .\end{array}