Chapter 1 - Equations and Inequalities - 1.6 Other Types of Equations and Applications - 1.6 Exercises - Page 147: 41

$13\frac{1}{3}\ hours$

Step 1. The inlet pipe would fill $1/5$ of the pool per hour. Step 2. The outlet pipe would empty $1/8$ of the pool per hour. Step 3. Together, they would fill $1/5-1/8=3/40$ of the pool per hour. Step 4. With both open, the pool will be filled in $40/3=13\frac{1}{3}\ hours$