Chapter 9 - Basic Algebra - 9.2 Adding and Subtracting Signed Numbers - 9.2 Exercises - Page 638: 18

-25

To add $-5+(-20)$, we can take the absolute value of both numbers. $|-5|=5$ $|-20|=20$ To add two negative numbers, we can add the absolute value of both numbers and then add a negative sign in front of the result. $|-5|+|-20|=5+20=25$ Therefore, $-5+(-20)=-25$.