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      Question

      A submarine can navigate 112 km upstream and 130 km

      downstream, and it takes a total of 8 hours and 6 minutes to complete this journey. Now, the task is to calculate the time required for the submarine to travel 64 km upstream and 195 km downstream, taking into account that the ratio of the submarine's speed in still water to the speed of the stream is 9:4.
      A 6 hrs 45 min Correct Answer Incorrect Answer
      B 2 hrs 57 min Correct Answer Incorrect Answer
      C 6 hrs 57 min Correct Answer Incorrect Answer
      D 8 hrs 57 min Correct Answer Incorrect Answer
      E none of these Correct Answer Incorrect Answer

      Solution

      ATQ, Let, speed of Submarine in still water and speed of stream is ‘9a’ km/h and ‘4a’ km/h, respectively. Upstream speed = 9a – 4a = 5a km/h Downstream speed = 9a + 4a = 13a km/h So, 112/5a + 130/13a = 81/10 Or, (22.4 + 10) × 10/81 = a Or, a = 4 Upstream speed = 5 × 4 = 20 km/h Downstream speed = 13 × 4 = 52 km/h Desired time = (64/20) + (195/52) = 3.2 + 3.75 = 6 hrs 57 minutes

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