A boatman goes 2 km against the current of the stream in 1 hour and goes 1 km along the current in 10 minutes. How long will it take to go 5 km in stationary water?
A. 40 minutes
B. 1 hour
C. 1 hour 15 min
D. 1 hour 30 min

• speed (upstream) =2/1 = 2 kmhr
  speed (downstream)=1/(10/60)= 6 kmhr
  
  speed in still water = 1/2 (2+6) = 4 kmhr
  
  time taken in stationary = 5/4 = 1 hrs 15 min
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