Correct Answer - Option 4 : 12 hours
Given:
Time taken by pipe A to fill the tank = 3 hours
Time taken by pipe B to fill the tank = 4 hours
Time taken by pipe C to empty the tank = 2 hours
Concept:
If a tap can fill a tank in x hours, then the tank filled by the tap in 1 hour = 1 / x of the total tank.
Calculation:
Part of tank filled in 1 minute when all three pipes are opened simultaneously
⇒ (1 / 3) + (1 / 4) – (1 / 2)
⇒ (4 + 3 – 6) / 12
⇒ 1 / 12
∴ The tank can be filled in 12 hours.