Pipes A and B can fill a tank in 15 hours and 25 hours, respectively, whereas pipe C can empty the full tank in 40 hours. All three pipes are opened together, but pipe A is closed after 5 hours. After how many hours will the remaining part of the tank be filled?
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e. .
Let the total capacity of the tank = 600 (LCM of 15, 25, and 40)
Efficiency of pipe A = 600/15 = 40 units/hour
Efficiency of pipe B = 600/25 = 24 units/hour
Efficiency of pipe C = 600/40 = 15 units/hour
Total efficiency = 40 + 24 - 15 = 49 units/hour
Filled in 5 hours = 49 × 5 = 245 units
Remaining part = 600 - 245 = 355 units
Efficiency of pipes B and C = 24 - 15 = 9 units/hour
Time required for pipes B and C = 355/9 = hours
Therefore, the remaining part of the tank should be filled in hours.