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    Question

    A bath can be filled by the cold water pipe in 20 hrs and by the hot water in 30 hrs. Mohit leaves the bathroom after turning on both pipes simultaneously and returns at the moment when the bath should be full. Finding however, that the waste pipe has been open, he now closed it. In 8 hrs more, the bath is full. In what time would the waste pipe empty it?

    A 16 hours Correct Answer Incorrect Answer
    B 24 hours Correct Answer Incorrect Answer
    C 18 hours Correct Answer Incorrect Answer
    D 12 hours Correct Answer Incorrect Answer

    Solution

    A B 20 30 LCM = 60 units Eff 3 : 2 So (A+B)`xx` 12 =(A+B+C)`xx` 12 +(A+B)`xx` 8

    (A+B)`xx` 4 =(A+B+C)`xx` 12
    A+B =3(A+B+C) 3+2 = 3(3+2+C) 5/3 = 5+C So C = 5/3-5 = -10/3 So waste pipe C can empty whole tank in = 60/(10/3) = 18hrs

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