Question
Pipe ‘A’ takes 10 minutes to fill a tank.
Pipe ‘B’ takes 20 minutes to empty the same tank. If pipe ‘B’ is opened 4 minutes after pipe ‘A’, then find the total time taken to fill the tank in this manner.Solution
Let the capacity of the tank be ‘20’ litres {LCM (10, 20)} Efficiency of pipe ‘A’ = (20/10) = 2 litres/minute Efficiency of pipe ‘B’ = (20/20) = 1 litres/minute Quantity of water filled by pipe ‘A’ in 4 minutes = 4 × 2 = 8 litres Quantity of water to be filled = 20 – 8 = 12 litres Time taken by pipe ‘A’ and ‘B’ together to fill 12 litres of water = {12/(2 – 1)} = 12 minutes Total time taken = 4 + 12 = 16 minutes
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