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    Question

    Pipes X and Y can fill a water tank individually in 24

    minutes and 36 minutes, respectively. A third pipe Z can empty the tank in 72 minutes. If all three pipes are opened at the same time, how long (in seconds) will it take to fill the tank?
    A 2571 secs Correct Answer Incorrect Answer
    B 1332 secs Correct Answer Incorrect Answer
    C 1080 secs Correct Answer Incorrect Answer
    D 1200 secs Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    ATQ,

    Let the capacity of the tank be 72 litres (LCM of 24, 36, and 72)

    Efficiency of X = 72 ÷ 24 = 3 litres/minute

    Efficiency of Y = 72 ÷ 36 = 2 litres/minute

    Efficiency of Z = 72 ÷ 72 = 1 litre/minute (outlet)

    Required time = 72 ÷ (3 + 2 - 1) = 72 ÷ 4 = 18 minutes = 18 × 60 = 1,080 seconds

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