Expression with signed integers

Statement

Compute the value of the expression $\big((-4)-(-9)\big)\times\big(3+(-8)\big).$

Solution

First work out the two brackets, then the product: $\begin{aligned} (-4)-(-9) &= -4+9 = 5, \ 3+(-8) &= -5, \[4pt] 5\times(-5) &= \boxed{-25}. \end{aligned}$ The product of a positive number and a negative number is negative.