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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 7.5 hours to travel 750 km downstream, then find the time taken by boat ‘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 ‘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 = 750/7.5 Or, 10x = 100 Or, x = 10 Therefore, upstream speed of boat ‘B’ = 9x – 2x = 7x = 70 km/hr Downstream speed of boat ‘B’ = 9x + 2x = 11x = 110 km/hr Required time taken = (210/70) + (330/110) = 3 + 3 = 6 hours

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