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    Question

    Pipe β€˜A’ can fill a tank in 20 hours whereas leak

    β€˜A’ can empty it in 30 hours. If they both operate along with pipe β€˜B’, then the given tank gets filled in 15 hours. How much time is needed to fill the given tank if pipe β€˜B’ and leak β€˜A’ work together?Β Β 
    A 40 hours Correct Answer Incorrect Answer
    B 60 hours Correct Answer Incorrect Answer
    C 75 hours Correct Answer Incorrect Answer
    D 30 hours Correct Answer Incorrect Answer
    E 84 hours Correct Answer Incorrect Answer

    Solution

    Let the capacity of the tank be 60 litres {LCM (20 and 30)} Efficiency of pipe β€˜A’ = 60 Γ· 20 = 3 litres/hour Efficiency of leak β€˜A’ = 60 Γ· 30 = 2 litres/hour Combined efficiency of pipe β€˜A’ and leak β€˜A’ = 3 – 2 = 1 litre/hour Combined efficiency of pipe β€˜A’, β€˜B’ and leak β€˜A’ = 60 Γ· 15 = 4 units/hour Efficiency of pipe β€˜B’ = 4 – 1 = 3 units/hour Time taken by pipe β€˜B’ and leak β€˜A’ to fill the tank = 60 Γ· (3 – 2) = 60 hours

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