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    Question

    The ratio of the speed of boats β€˜A’ and β€˜B’ in

    still water is 8:9, respectively. The speed of the current is 25% of the speed of boat β€˜A’ in still water. If boat β€˜A’ takes 7.5 hours to travel 750 km downstream, then find the time taken by boat β€˜B’ to travel 210 km upstream and 330 km downstream. (Note: Both the boats are rowing in the same stream.)
    A 2 hours Correct Answer Incorrect Answer
    B 8 hours Correct Answer Incorrect Answer
    C 6 hours Correct Answer Incorrect Answer
    D 12 hours Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    Let the speeds of boats β€˜A’ and β€˜B’ in still water be 8x km/hr and 9x km/hr Therefore, speed of the current = 0.25 Γ— 8x = 2x km/hr According to the question, 8x + 2x = 750/7.5 Or, 10x = 100 Or, x = 10 Therefore, upstream speed of boat β€˜B’ = 9x – 2x = 7x = 70 km/hr Downstream speed of boat β€˜B’ = 9x + 2x = 11x = 110 km/hr Required time taken = (210/70) + (330/110) = 3 + 3 = 6 hours

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