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      Question

      A boat has a speed of 30 m/s in still water. When moving

      upstream, its speed is reduced by 16(2/3) % compared to its still water speed. If the speed of the stream increases by 60% and the boat's speed in still water increases by 40%, determine the total time required for the boat to travel 680 meters downstream and then return 680 meters upstream.
      A 54 sec Correct Answer Incorrect Answer
      B 66 sec Correct Answer Incorrect Answer
      C 72 sec Correct Answer Incorrect Answer
      D 33.6 sec Correct Answer Incorrect Answer
      E None of these Correct Answer Incorrect Answer

      Solution

      Speed of boat in still water = 30 m/c

      So, upstream speed of boat = 30 X (5/6) = 25 m/s

      So, speed of stream = 30 - 25 = 5 m/s

      Increased speed of stream = 5 X 1.6 = 8 m/s

      Increased speed of boat in still water = 30 X 1.4 = 42 m/s
      So, Required time = {680/(42 + 8) } + {680/(42 - 8) }

      = 13.6 + 20 = 33.6 = 33.6 sec

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