A boat travels at 8 km/hr in still water and water flows at 4 km/hr. The speed of the boat if it goes against the water stream is?
4 km/hr
Consider, a boat moving at a speed of S1 and the speed of the water stream is S2.
If the stream and boat are moving in the same direction(Downstream or along the stream), the Effective speed of the boat = S1 + S2
And, If the stream and boat are moving in the opposite direction(Upstream or against the stream), the Effective speed of the boat = S1 - S2
Here, Boat and stream go in the opposite direction(upstream), So, Effective speed = 8 km/hr - 4 km/hr = 4 km/hr