Two pipes fill a tank in 6 and 9 hours. Both are opened together. How long do they take to fill $\frac{5}{6}$ of the tank?

Explanation

1. 01

   Together: $\frac{1}{6} + \frac{1}{9} = \frac{5}{18}$ of the tank an hour.

2. 02

   $\frac{5}{6} \div \frac{5}{18} = 3$ hours.