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    Question

    Three pipes A, B and C are connected to a reservoir.

    Pipe A can fill it in 16 minutes, pipe B in 24 minutes, while pipe C can empty it in 12 minutes. Pipe A is opened first, pipe B after 4 minutes, and pipe C after 8 minutes. Find the total time taken to fill the reservoir.
    A 12 min Correct Answer Incorrect Answer
    B 16 min Correct Answer Incorrect Answer
    C 20 min Correct Answer Incorrect Answer
    D 24 min Correct Answer Incorrect Answer
    E 28 min Correct Answer Incorrect Answer

    Solution

    Let the capacity of the reservoir be 48 litres. {LCM (16, 24 and 12)}
    So, efficiency of inlet pipe A = 48 ÷ 16 = 3 litres/minute
    And, efficiency of inlet pipe B = 48 ÷ 24 = 2 litres/minute
    And, efficiency of outlet pipe C = 48 ÷ 12 = 4 litres/minute
    In first 4 minutes, pipe A will fill 4 × 3 = 12 litres
    And, pipes A and B together will fill 4 × (3 + 2) = 20 litres
    So, required time = 4 + 4 + {(48 − 12 − 20) ÷ (3 + 2 − 4)} = 24 minutes

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