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      Question

      Speed of the boat in still water and the downstream

      speed of the boat are in the ratio of 5:6 respectively. The boat covers 80 km upstream and 72 km downstream in 8 hours. Find the time taken by the boat to cover 150 km in still water.
      A 7.5 hrs Correct Answer Incorrect Answer
      B 8.5 hrs Correct Answer Incorrect Answer
      C 3.5 hrs Correct Answer Incorrect Answer
      D 2.4 hrs Correct Answer Incorrect Answer
      E None of these Correct Answer Incorrect Answer

      Solution

      ATQ,

      Let the speed of the boat in still water and speed of the stream be x km/h and y km/h respectively. According to the question: x + y = 6x / 5 5x + 5y = 6x x = 5y So the upstream speed and downstream speed of the boat are 4y and 6y respectively. So according to question: 80 / 4y + 72 / 6y = 8 20/y + 12/y = 8 32/y = 8 → y = 4 So the speed of the boat in still water = 5 × 4 = 20 km/h Time to cover 150 km in still water = 150 / 20 = 7.5 hours

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