Question

A,b,c are three pipes attach to a tank. A and b can fill in 20 min and 30 min respectively. While c can empty in 15 min. If a, b, c kept open alternatively for 1 minute each. How will tank will be filled.

Answer 1

Pipe A takes 20 minutes

In one minute pipe A will fill 1/20 th part of the tank

Pipe B takes 30 minutes to fill the tank

In one minute it will fill 1/30 th part of the tank

Pipe C takes 15 minutes to empty the tank

In one minute it will empty 1/15th part of the tank

Now Tank filled by Pipe A and Pie B together in One Minute = (1/20) + (1/30)

Tank will be filled when three pipes are open alternately

(1/20) + (1/30) - (1/15)

= 1/60th part of the tank will be filled  

So it took 3 minutes to fill 1/60th part of the tank

To fill whole tank time taken = ( 1 ÷ 1/60)×3 = 180 minutes or 3 hours