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      Question

      The speed of boat 'A' in upstream and still water is in the

      ratio of 3:5. The boat takes 16 hours to travel 175 km downstream and 275 km in still water. The still water speed of boat 'B' is 20% less than that of boat 'A'. If the speed of the stream increases by 20%, determine the time required for boat 'B' to cover 480 km downstream and 360 km upstream.
      A 60 hours Correct Answer Incorrect Answer
      B 48 hours Correct Answer Incorrect Answer
      C 56 hours Correct Answer Incorrect Answer
      D 64 hours Correct Answer Incorrect Answer
      E None of these Correct Answer Incorrect Answer

      Solution

      Let the upstream speed and still water speed of boat 'A' be 3x km/hr and 5x km/hr.

      So, the downstream speed of boat 'A' = (5x - 3x + 5x) = 7x km/hr

      Speed of stream = (5x - 3x) = 2x km/hr

      ATQ,

      (175/7x) + (275/5x) = 16

      So, (25/x) + (55/x) = 16

      So, (80/x) = 16

      So, 'x' = 5

      So, still water speed of boat 'A' = 5 X 5 = 25 km/hr

      Still water speed of boat 'B' = 25 X 0.8 = 20 km/hr

      Increased speed of stream = 2 X 5 X 1.2 = 12 km/hr

      So, required time = {480 ÷ (20 + 12) } + {360 ÷ (20 - 12)} = 15 + 45 = 60 hours

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