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    Question

    Two pipes, A and B, can fill a tank in 12 hours and 15

    hours respectively, while a third pipe, C, can empty the tank in 10 hours. If all three pipes are opened simultaneously, in how many hours will the tank be full?
    A 20 hours Correct Answer Incorrect Answer
    B 18 hours Correct Answer Incorrect Answer
    C 30 hours Correct Answer Incorrect Answer
    D 24 hours Correct Answer Incorrect Answer
    E 16 hours Correct Answer Incorrect Answer

    Solution

    Work done by A in 1 hour = 1/12,  Work done by B in 1 hour = 1/15 Work done by C in 1 hour (emptying) = -1/10 Net work done in 1 hour = (1/12) + (1/15) - (1/10) Taking LCM of 12, 15, and 10 = 60, Net work = (5/60) + (4/60) - (6/60)  = 3/60 = 1/20 The tank will be filled in 20 hours. Correct Option: a) 20 hours

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