A pipe fills $\frac{1}{3}$ of a tank in 4 hours. How much longer will it take to fill the rest?

Explanation

1. 01

   A third in 4 hours means the whole tank in 12 hours.

2. 02

   The rest is $\frac{2}{3}$ of the tank: $\frac{2}{3} \times 12 = 8$ hours.