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      Question

      A motor boat covers a certain distance downstream in a

      river in 2 hours. It covers the same distance upstream in 2 hours and 30 minutes. If the speed of water is 3.5 km/h, then the speed of the boat in still water is:
      A 16.25 km/hr Correct Answer Incorrect Answer
      B 27 km/hr Correct Answer Incorrect Answer
      C 32.5 km/hr Correct Answer Incorrect Answer
      D 31.5 km/hr Correct Answer Incorrect Answer
      E 13.5 km/hr Correct Answer Incorrect Answer

      Solution

      Let the speed of boat in still water be x km/hr and the distance be y km. Rate downstream = (x + 3.5) km/hr Rate upstream = (x – 3.5) km/hr According to the question, y/(x + 3.5) = 2 --- (i) y/(x – 3.5) = 5/2 --- (ii) On dividing equation (i) by (ii), (x – 3.5)/(x + 3.5) = 2/(5/2) = 4/5 5x – 16.5 = 4x + 15 x = 16.5 + 15 = 31.5 kmph

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