Question

A race-boat covers a distance of 60 km downstream in one and a half hour. It covers this distance up stream in 2 hours. The speed of the race-boat in still water is 35 km/hr, Find the speed of the stream.

• A. 5 km/hr
• B. 5 m/s
• C. 0.5 Km/s
• D. 6 Km/m

Answer 1

The correct option is A 5 km/hr

Given, distance covered = 60 km
Time taken in downstream = 1.5 hour and time taken in upstream = 2 hour
Therefore, speed downstream $=\frac{60}{1.5}=40km/h$
and speed upstream $=\frac{60}{2}=30km/h$
We know that, speed of the stream $=\frac{1}{2}(downstreamspeed-upstreamspeed)=\frac{1}{2}(40-30)=5km/h$