Chapter 1 - Introduction to Algebraic Expressions - 1.7 Multiplication and Division of Real Numbers - 1.7 Exercise Set - Page 58: 68

$-\dfrac{5}{2}$

The given expression, $ -2\div(0.8) $, simplifies to \begin{array}{l}\require{cancel} \dfrac{-2}{0.8} \\\\= \dfrac{-2}{0.8}\cdot\dfrac{10}{10} \\\\= \dfrac{-20}{8} \\\\= \dfrac{\cancel{4}\cdot(-5)}{\cancel{4}\cdot2} \\\\= \dfrac{-5}{2} \\\\= -\dfrac{5}{2} .\end{array}