Multiple choice

A man can row a distance of 720 meters against the stream in 12 minutes and returns to the starting point in 9 minutes. What is the speed (in km/h ) of the man in still water ?

  1. 4.2 km/hr

  2. 3.6 km/hr

  3. 4.8 km/hr

  4. 3.2 km/hr
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Speed against stream = 0.72 km / 0.2 h = 3.6 km/h. Speed with stream = 0.72 km / 0.15 h = 4.8 km/h. If v is speed in still water and u is stream speed, then v - u = 3.6 and v + u = 4.8. Solving: v = (3.6 + 4.8)/2 = 4.2 km/h.

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