QA – Placement Quizzes | Pipes and Cisterns | Question 10
Two pipes A and B are connected to drain out a water tank. A alone can drain out the tank in 20 hours and B can drain 20 liters per hour. Find the capacity of the water tank given that working together, they require 12 hours to completely drain out the tank.
Explanation: Let the capacity of the tank be LCM (20, 12) = 60 units
=> Efficiency of A working alone = 60 / 20 = 3 units / hour
=> Efficiency of A and B working together = 60 / 12 = 5 units / hour
Therefore, Efficiency of B working alone = Efficiency of A and B working together – Efficiency of A working alone
=> Efficiency of B working alone = 5 – 3 = 2 units / hour
=> Time required by B alone to drain the tank = 60 / 2 = 30 hours
But we are given that B can drain the tank at the rate of 20 liters per hour.
Therefore, capacity of the water tank = 20 x 30 = 600 liters
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