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      Question

      In still water, the speed ratio of boats A and B is

      10:7. Boat A’s still-water speed is twice the stream speed. If A covers 180 km downstream in 6 hours, how long will B take to go 72 km upstream?
      A 12 hrs Correct Answer Incorrect Answer
      B 18 hrs Correct Answer Incorrect Answer
      C 20 hrs Correct Answer Incorrect Answer
      D 10 hrs Correct Answer Incorrect Answer
      E None of these Correct Answer Incorrect Answer

      Solution

      ATQ, Let the speeds be 10x and 7x km/hr Stream speed = 10x/2 = 5x Downstream speed of A = 10x + 5x = 15x 180/6 = 30 β‡’ 15x = 30 β‡’ x = 2 Required time = 72/(7x – 5x) = 72/(2x) = 72/4 = 18 hours

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