A person can swim in still water at 4 km/h. If the speed of water 2 km/h, how…
2025
A person can swim in still water at 4 km/h. If the speed of water 2 km/h, how many hours will the man take to swim back against the current for 6km?
- A.
3
- B.
5
- C.
6
- D.
4
Show answer & explanation
Correct answer: A
Concept
When a person swims against a current (upstream), the current opposes the motion, so the effective speed is the swimmer's still-water speed minus the stream's speed: Upstream speed = Swimmer speed − Stream speed. The time to cover a distance equals distance divided by speed: Time = Distance / Speed.
Application
Still-water swimming speed, M = 4 km/h; stream speed, S = 2 km/h.
Swimming back against the current means swimming upstream, so the effective speed is Upstream speed = M − S = 4 − 2 = 2 km/h.
Distance to cover, D = 6 km.
Time = Distance / Upstream speed = 6 / 2 = 3 hours.
Cross-check
Multiplying the upstream speed by the computed time recovers the given distance: 2 km/h × 3 h = 6 km, confirming the answer.