## Basic College Mathematics (9th Edition)

$-\frac{3}{2}$
In order to subtract by changing subtraction to addition, we can follow the steps below. Step 1. The first number stays the same. Step 2. Change the subtraction sign to an addition sign. Step 3. Change the second number to its opposite. Step 4. Evaluate. Therefore, $-\frac{7}{10}-\frac{4}{5}=-\frac{7}{10}+(-\frac{4}{5})$. Before evaluating further, we must make sure both fractions have the same denominator, which is 10. $-\frac{7}{10}+(-\frac{4\times2}{5\times2})=-\frac{7}{10}+(-\frac{8}{10})=-\frac{15}{10}=-\frac{3}{2}$