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    Question

    A and B can fill a tank in 14 and 21 hours. Pipe C can

    empty it in ‘x’ hours. All three open together fill the tank in 7 hours. Find x.
    A 30 hours Correct Answer Incorrect Answer
    B 36 hours Correct Answer Incorrect Answer
    C 40 hours Correct Answer Incorrect Answer
    D 42 hours Correct Answer Incorrect Answer

    Solution

    Let the capacity of the tank = 84 liters (LCM of 14, 21, and 7)
    Amount of water filled by pipe A in one hour = 84 ÷ 14 = 6 liters
    Amount of water filled by pipe B in one hour = 84 ÷ 21 = 4 liters
    Amount of water filled by pipes A, B and C together in one hour = 84 ÷ 7 = 12 liters
    Amount of water taken by pipe C alone in one hour = 6 + 4 – 12 = 2 liters
    Time taken by pipe C alone to empty the tank = 84 ÷ 2 = 42 hours

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