New Enroll in RBI Grade B New Batch - Starts on May 21

    Question

    There are two inlet pipes 'A', 'B' and one outlet pipe 'C'

    in a tank. ‘A’ and ‘B’ can fill the tank in 24 minutes and 16 minutes respectively. ‘C’ is 50% less efficient than ‘A’. If ‘A’ and ‘C’ are open together but after 12 minutes ‘A’ is replaced with ‘B’, then find the total time required to fill the tank completely.
    A 25 minutes Correct Answer Incorrect Answer
    B 28 minutes Correct Answer Incorrect Answer
    C 30 minutes Correct Answer Incorrect Answer
    D 32 minutes Correct Answer Incorrect Answer
    E 35 minutes Correct Answer Incorrect Answer

    Solution

    Let the total capacity of the tank be 48x units (LCM of 24 and 16).
    Efficiency of A = 48x / 24 = 2x units/min
    Efficiency of B = 48x / 16 = 3x units/min
    Efficiency of C = 50% of 2x = 1x units/min
    Tank filled in first 12 minutes = (2x - 1x) × 12 = 12x units
    Remaining = 48x - 12x = 36x units
    Time = 36x / (3x - 1x) = 36x / 2x = 18 minutes
    Total time = 12 + 18 = 30 minutes

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