2026 · Q24
A boatman can row to a place (Y) at a distance of 24 km from the starting point (X) and back in 14 hours. If he can row 4 km with the stream in the same time as he can row 3 km against it, what is the speed of the stream?
Elementary MathematicsTime, Speed and Distance
- A0.5 km/hr
- B1 km/hr
- C2 km/hr
- D2.5 km/hr
Explanation
Let b be the boat's speed and s the stream's speed. Rowing 4 km downstream takes the same time as 3 km upstream, so 4/(b + s) = 3/(b − s), giving b = 7s. The round trip of 24 km each way takes 24/(b + s) + 24/(b − s) = 24/(8s) + 24/(6s) = 7/s = 14 hours. Thus s = 0.5 km/h, option A.