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    Question

    Two pipes, A and B, together can fill a tank in 24

    minutes. Both the pipes were opened together, but pipe A, which can fill the tank in 40 minutes, was closed 30 minutes before the tank got filled. In how many minutes did the tank get filled?
    A 38 Correct Answer Incorrect Answer
    B 42 Correct Answer Incorrect Answer
    C 40 Correct Answer Incorrect Answer
    D 45 Correct Answer Incorrect Answer

    Solution

    Pipes A and B, together can fill a tank in 24 minutes Pipe A can fill the tank in 40 minutes Let the total capacity of tank be 120 (LCM of 24 and 40) (A + B)'s efficency = 120/24 = 5 A's efficency = 120/40 = 3  B's efficiency = 5 - 3 = 2 Now, Tank filled by B when A is closed = 30 × 2 = 60 so A and B filled  the tank before A was closed = 60/5 = 12 min therefore, tank can be filled in 30 + 12 = 42 min

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