Answer
$-\dfrac{3}{8}$
Work Step by Step
Using operations on real numbers, the given expression, $
\left(-\dfrac{1}{2}\right)+\dfrac{1}{8}
,$ evaluates to
\begin{array}{l}\require{cancel}
-\dfrac{1}{2}+\dfrac{1}{8}
\\\\=
-\dfrac{4}{8}+\dfrac{1}{8}
\\\\=
\dfrac{-4+1}{8}
\\\\=
\dfrac{-3}{8}
\\\\=
-\dfrac{3}{8}
.\end{array}