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

    Question

    An empty tank can be filled by an inlet pipe in 10

    hours, while an outlet pipe can empty it in 15 hours. If we open (N - 1) outlet pipes of the same capacity and (N + 1) inlet pipes also of the same capacity, the tank is filled in 3 hours. Determine the number of inlet pipes used.
    A 4 Correct Answer Incorrect Answer
    B 5 Correct Answer Incorrect Answer
    C 6 Correct Answer Incorrect Answer
    D 3 Correct Answer Incorrect Answer
    E 7 Correct Answer Incorrect Answer

    Solution

    Let the capacity of tank be 30 litres (LCM of 10 and 15) Efficiency of 1 inlet pipe = (30/10) = 3 units/litre Efficiency of 1 outlet pipe = (30/15) = 2 units/litre ATQ, {3 X (N + 1) - 2 X (N - 1) } X 3 = 30 Or, (3N + 3 - 2N + 2) X 3 = 30 Or, N + 5 = 10 So, 'N' = 5 Required number of inlet pipes used = (n + 1) = 5 + 1 = 6

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