Question
Pipe 'A' alone can fill a cistern
in 20 minutes. If pipes 'A' and 'B' are opened together, it takes 25 minutes to fill the cistern. Find the time taken by pipe 'B' alone to empty 50% of the cistern.Solution
ATQ, Total capacity of the tank = L.C.M of 20 and 25 = 100 units. Efficiency of pipe 'A' alone = 100 ÷ 20 = 5 units/minute. Combined efficiency of pipes 'A' and 'B' = 100 ÷ 25 = 4 units/minute. Efficiency of pipe 'B' alone = 4 - 5 = -1 unit/minute (outlet). Time taken by pipe 'B' alone to empty 50% of the cistern = (100 × 0.5) ÷ 1 = 50 minutes.
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