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

    Question

    A boat can cover 84 km in upstream in 2 hours, if the

    speed of the stream is 30% of the speed of boat in still water, then find the time taken by the boat to cover 156 km in downstream.
    A 1 hours Correct Answer Incorrect Answer
    B 2 hours Correct Answer Incorrect Answer
    C 3 hours Correct Answer Incorrect Answer
    D 4 hours Correct Answer Incorrect Answer

    Solution

    Let the speed of boat in still water be ‘x’ km/h
    Speed of stream = 0.30 × x = ‘0.3x’ km/h
    Speed of boat in upstream = x – 0.3x = 0.7x km/h
    So, 0.7x = 84/2
    Or, 0.7x = 42
    Or, x = 60
    So, speed of boat in still water = 60 km/h
    And, speed of stream = 60 × 0.3 = 18 km/h
    Time required to cover 156 km in downstream = {156/(18 + 60)} = 2 hours

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