Chapter 1 - Introduction to Algebraic Expressions - 1.6 Subtraction of Real Numbers - 1.6 Exercise Set - Page 49: 26

-48.2

The opposite of a real number $a$ is $-a$. For any two numbers $a$ and $-a$, $a+(-a)=0$. That is, the sum of a number and its opposite is equal to 0. Therefore, the opposite of 48.2 is -48.2, because $48.2+(-48.2)=0$.