A boat can travel at 13 km/h in still water. The stream flows at 4 km/h. Find the time taken to travel 68 km downstream.

Given data

• Still-water speed u = 13 km/h
• Stream speed v = 4 km/h
• Distance downstream = 68 km

Concept / Approach

• Downstream speed = u + v.
• Time = Distance / Speed.

Step-by-step calculation

Downstream speed = 13 + 4 = 17 km/hTime = 68 / 17 = 4 hours

Verification

17 × 4 = 68, consistent.

Common pitfalls

• Using u − v (upstream) by mistake.

Final Answer

4 hours