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    Question

    The ratio of the speed of boats ‘A’ and ‘B’ in

    still water is 8:9, respectively. The speed of the current is 25% of the speed of boat ‘A’ in still water. If boat ‘A’ takes 12 hours to travel 600 km downstream, then find the time taken by boat ‘B’ to travel 140 km upstream and 550 km downstream. (Note: Both the boats are rowing in the same stream.)
    A 10 hours Correct Answer Incorrect Answer
    B 12 hours Correct Answer Incorrect Answer
    C 14 hours Correct Answer Incorrect Answer
    D 15 hours Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    Let the speeds of boats ‘A’ and ‘B’ in still water be 8x km/hr and 9x km/hr Therefore, speed of the current = 0.25 × 8x = 2x km/hr According to the question, 8x + 2x = 600/12 Or, 10x = 50 Or, x = 5 Therefore, upstream speed of boat ‘B’ = 9x – 2x = 7x = 35 km/hr Downstream speed of boat ‘B’ = 9x + 2x = 11x = 55 km/hr Required time taken = (140/35) + (550/55) = 4 + 10 = 14 hours

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