If pipe A can fill a cistern in 50 hours and pipe B can empty \(\frac{1}{3}\)rd part of the same tank in 80 hours. They are opened for 2 hours and then A is closed. Find the time taken by B to empty the tank.

7.6 hours

Time taken to fill the full tank by A → 50 hrs

Time taken to empty the full tank by B → 80 × 3 = 240 hrs

Efficiency of (A + B) = 24 - 5 = 19

In two hours, quantity of water filled = 19 × 2 = 38 ltrs

Time taken by B to empty it = \(\frac{38}{5}\) = 7.6 hours