Multiple choice

A man can row a boat 30 km. upstream and 44 km. down stream in 10 hours. Also he can row the boat 40 km. upstream and 55 km. down stream in 13 hours. Find the speed of the man in still water?

  1. 3 km./hr.

  2. 8 km./hr.

  3. 10 km./hr.

  4. 6 km./hr.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let upstream speed = u, downstream = d, boat speed in still water = b, current speed = c. Then u = b-c, d = b+c. From given data: 30/u + 44/d = 10 and 40/u + 55/d = 13. Solving: u = 5, d = 11. Then b = (u+d)/2 = (5+11)/2 = 8 km/hr. Option B is correct.

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