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      Question

      A boat travels 100 km upstream and 160 km downstream in 9

      hours. If the speed of the boat in still water is 25 km/hr greater than the speed of the stream, calculate the stream's speed.
      A 4.5 km/hr Correct Answer Incorrect Answer
      B 5.5 km/hr Correct Answer Incorrect Answer
      C 1.5 km/hr Correct Answer Incorrect Answer
      D 3.5 km/hr Correct Answer Incorrect Answer
      E None of these Correct Answer Incorrect Answer

      Solution

      ATQ,

      Let the speed of the stream = x

      And the speed of the boat in still water = x + 25

      100/(x + 25 – x) + 160/(x + 25 + x) = 9

      100/25 + 160/(2x + 25) = 9

      4 + 160/(2x + 25) = 9

      160/(2x + 25) = 9 – 4

      160/(2x + 25) = 5

      2x + 25 = 160/5

      2x + 25 = 32

      2x = 32 – 25

      2x = 7

      x = 7 / 2

      x = 3.5

      The speed of the stream = 3.5 km/hr

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