The speed of a boat in still water is 10 km/hr. If it can travel 26 km downstream and 14 km upstream at the same time, the speed of the stream is-

Answer: Option C

Let the speed of the stream be x km/hr
Then speed downstream = (10 + x) km/hr
Speed upstream
$$\begin{array}{rl}& \text{ = }\left(10-x\right)km/hr\\ & \therefore \frac{26}{\left(10+x\right)}=\frac{14}{\left(10-x\right)}\\ & \Rightarrow 260-26x=140+14x\\ & \Rightarrow 40x=120\\ & \Rightarrow x=3km/hr\end{array}$$