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    Question

    Two inlet pipes, each with the same capacity, can fill

    an empty tank 'A' together in 20 minutes. There is also an outlet pipe that can empty 40% of the tank 'A' in 10 minutes. If we open just one of these inlet pipes and the outlet pipe simultaneously to drain a completely filled tank 'B'—which holds three times the volume of tank 'A'—how long will it take to empty tank 'B'?
    A 150 minutes Correct Answer Incorrect Answer
    B 200 minutes Correct Answer Incorrect Answer
    C 400 minutes Correct Answer Incorrect Answer
    D 100 minutes Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    Total time taken by outlet pipe to empty the tank 'A' = 10 X (100/40) = 25 minutes Let the capacity of tank 'A' be 100 units (L.C.M. of 20 minutes and 25 minutes) Total efficiency of two inlet pipes = (100/20) = 5 units/minute Efficiency of one inlet pipe = 2.5 units/minute Efficiency of outlet pipe = (100/25) = - 4 units/minute Combined efficiency of one inlet and one outlet pipe = 2.5 - 4 = - 1.5 (' - ' sign denotes efficiency of outlet pipe is more than the inlet pipe) Capacity of tank 'B' = (100 X 3) = 300 units Required time = (300/1.5) = 200 minutes

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