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    Question

    Pipes 'E' and 'F' can fill a tank in 20 and 25 minutes

    respectively. Both are opened together. A leak develops after half of the tank is filled, which removes (1/5)th of the incoming water. Calculate the total time taken to fill the tank.
    A 11.5 Correct Answer Incorrect Answer
    B 13.25 Correct Answer Incorrect Answer
    C 12.5 Correct Answer Incorrect Answer
    D 10.75 Correct Answer Incorrect Answer

    Solution

    Capacity = 100 litres (LCM of 20 and 25)
    'E' = 100 ÷ 20 = 5 litres/min
    'F' = 100 ÷ 25 = 4 litres/min
    Time to half fill = (0.5 × 100) ÷ (5 + 4) = 50 ÷ 9 = 5.56 minutes
    Effective rate = (4/5) × (5 + 4) = 7.2 litres/min
    Time to fill remaining = 50 ÷ 7.2 = 6.94 minutes
    Total time = 5.56 + 6.94 = 12.5 minutes

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