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    Question

    The ratio of the speed of boats тАШAтАЩ and тАШBтАЩ in

    still water is 8:9, respectively. The speed of the current is 25% of the speed of boat тАШAтАЩ in still water. If boat тАШAтАЩ takes 10 hours to travel 500 km downstream, then find the time taken by boat тАШBтАЩ to travel 70 km upstream and 275 km downstream. (Note: Both the boats are rowing in the same stream.)
    A 5 hours Correct Answer Incorrect Answer
    B 3 hours Correct Answer Incorrect Answer
    C 4 hours Correct Answer Incorrect Answer
    D 7 hours Correct Answer Incorrect Answer

    Solution

    Let the speeds of boats тАШAтАЩ and тАШBтАЩ in still water be 8x km/hr and 9x km/hr Therefore, speed of the current = 0.25 ├Ч 8x = 2x km/hr According to the question, 8x + 2x = 500/10 Or, 10x = 50 Or, x = 5 Therefore, upstream speed of boat тАШBтАЩ = 9x тАУ 2x = 7x = 35 km/hr Downstream speed of boat тАШBтАЩ = 9x + 2x = 11x = 55 km/hr Required time taken = (70/35) + (275/55) = 2 + 5 = 7 hours

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