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    Question

    Pipe A fills a tank in 60 minutes, and pipe B can do it

    in 90 minutes. There’s also a pipe C that drains the tank in 180 minutes. If all three pipes are opened simultaneously, how long will it take to fill the tank?
    A 25 mins Correct Answer Incorrect Answer
    B 45 mins Correct Answer Incorrect Answer
    C 30 mins Correct Answer Incorrect Answer
    D 18 mins Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    ATQ,

    Let the total capacity of tank be 180 litres (LCM of 60, 90 and 180) Efficiency of A = 180 ÷ 60 = 3 litres/minute Efficiency of B = 180 ÷ 90 = 2 litres/minute Efficiency of C = 180 ÷ 180 = –1 litre/minute Net efficiency = 3 + 2 – 1 = 4 litres/minute Required time = 180 ÷ 4 = 45 minutes

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