Math Problem Solver

$${2}^{-1} - 3 = - \frac{5}{2} = -2.5$$

The sum can be computed by rewriting each term over a common denominator, where the least common denominator of $\frac{1}{2}$ and $\frac{-3}{1}$ is $2$. $$\begin{aligned} {2}^{-1} - 3 &= \frac{1 \cdot 1}{2 \cdot 1} + \frac{-3 \cdot 2}{1 \cdot 2} \\ &= \frac{1 + -6}{2} \\ &= \frac{-5}{2} \end{aligned}$$