Downstream and upstream speeds — Aptitude Question
Downstream and upstream speeds: A boat's speed in still water is 15 km/h and the stream flows at 3 km/h. Answer and worked solution on CodeKairo.
- Topic: Time, Speed & Distance
- Section: Quantitative Aptitude
- Difficulty: Easy
- Time target: 40 seconds
Question
A boat's speed in still water is 15 km/h and the stream flows at 3 km/h. What are its downstream and upstream speeds?
Options
- 12 and 18 km/h
- 15 and 3 km/h
- 18 and 12 km/h
- 18 and 15 km/h
Show the answer and the worked solution
Correct answer: C. 18 and 12 km/h
Worked solution
- Downstream = 15 + 3 = 18 km/h.
- Upstream = 15 − 3 = 12 km/h.
Answer: 18 and 12 km/h.
The idea
Downstream = boat + stream, upstream = boat − stream. Keep the order the question asks for.
Shortcut. Downstream is always the larger figure and the pair must average to the still-water 15, which only 18 and 12 does in the order asked.
Common trap. 12 and 18 km/h — the right numbers in the wrong order; the question asks for downstream first, and downstream is the faster 18.