Two pipes A and B can fill a cistern in 01 hour and 75 minutes respectively. There is also an outlet pipe C. If all the three pipes are opened together, the cistern is full in 50 minutes. How much time pipe C will take to empty a full tank?

100 min

Total efficiency of A + B + C = 6

Total efficiency of A + B = 5 + 4 = 9 

Efficiency of C = -3 ( it empties the cistern ) 

Total work = Efficiency × Time 

Time taken by C to empty the cistern = \(\frac{300}{3}\) = 100 min