Question
Two inlet pipes 'A' and 'B' can fill an empty tank in 30
minutes and 40 minutes, respectively. Another outlet pipe 'C' can empty the tank in 120 minutes. If all the three pipes are opened together, then find the time taken by them to fill the tank.Solution
Let the total capacity of the tank be 120 litres (LCM of 30, 40, and 120).
Efficiency of 'A' = 120 ÷ 30 = 4 litres/minute
Efficiency of 'B' = 120 ÷ 40 = 3 litres/minute
Efficiency of 'C' = 120 ÷ 120 = -1 litre/minute
Required time = 120 ÷ (4 + 3 - 1) = 120 ÷ 6 = 20 minutes
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