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    Question

    The diameters of three inlet pipes of a cistern are 1.5

    cm, 2 cm and 2.5 cm respectively. The pipe with the maximum diameter can alone fill up the cistern in 3 hours and 36 minutes. Find the time in which the empty cistern will be filled if all the three inlet pipes are opened together.
    A 1 hour 36 minutes Correct Answer Incorrect Answer
    B 1 hour 48 minutes Correct Answer Incorrect Answer
    C 216/235 hours Correct Answer Incorrect Answer
    D 235/216 hours Correct Answer Incorrect Answer

    Solution

    Diameters of three inlet pipes of a cistern = 1.5 : 2 : 2.5 = 3:4:5 Ratio of efficiency will be = Square of diameter => 9 : 16 : 25 Total work = Time x Maximum diameter efficiency = 216 min x 25 If all three work = (216 x 25)/50(9+16+25) = 108 min = 1 hour 48 min

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