A boat travels against the current from city X to city Y and with the current from city Y to city X ...........

Quantitative Aptitude (RRB NTPC) Time & distance

A boat travels against the current from city X to city Y and with the current from city Y to city X. If the speed of boat in still water is 40 km/hr and speed of current is 10 km/hr then find the average speed of the boat for the entire journey.

36.5 km/hr

34.5 km/hr

37.5 km/hr

33.33 km/hr

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Explanation:

When the distance travelled is same with two different speeds, the average speed is = 2ab/(a+b)
Where a and b are the two different speeds
Speed of boat in downstream = 40+10= 50 km/hr
Speed of boat in upstream = 40-10 = 30km/hr
So average speed of boat =(2×50×30)/(50+30)=37.5 km/hr