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A man can row 9 1/3 km/hr in still water and he finds that is thrice as much time to row u p than as to row down the same distance in river. The speed of the current is:________?

Correct answer: D. 4 2/3 km/hr

  • A. 3 1/3 km/hr
  • B. 3 1/9 km/hr
  • C. 1 ¼ km/hr
  • D. 4 2/3 km/hr

Explanation

Let v = 9 1/3 km/h = 28/3 km/h be the still-water speed and c be the current speed. Three times as much upstream time means the downstream speed is three times the upstream speed: v + c = 3(v - c), giving c = v/2 = 14/3 km/h = 4 2/3 km/h. The likely mistake is choosing 3 1/3 kmph by applying the time ratio directly to the current.

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