Delhi Police Constable Exam Model Paper 8

Given:
Pipe A can fill a tank in = 10 hrs
Pipe B can fill a tank in = 15 hrs
Pipe C can empty the full tank in = 5 hrs
Formula:
Total work = Efficiency × Time
Calculation:
Let total capacity be 30 units (LCM of 10, 15 and 5)
Efficiency of A = 3 units/hrs
Efficiency of B = 2 units/hrs
Efficiency of C = -6 units/hrs
Total efficiency of A, B and C = 3 + 2 – 6 = (-1) units/day
If all three pipe open together, then time taken to empty full tank = 30/1 = 30 hrs