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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 10 hours to travel 700 km downstream, then find the time taken by boat β€˜B’ to travel 147 km upstream and 770 km downstream. (Note: Both the boats are rowing in the same stream.)
    A 13 hours Correct Answer Incorrect Answer
    B 10 hours Correct Answer Incorrect Answer
    C 7 hours Correct Answer Incorrect Answer
    D 9 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 = 700/10 Or, 10x = 70 Or, x = 7 Therefore, upstream speed of boat β€˜B’ = 9x – 2x = 7x = 49 km/hr Downstream speed of boat β€˜B’ = 9x + 2x = 11x = 77 km/hr Required time taken = (147/49) + (770/77) = 3 + 10 = 13 hours

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