Two speeds on one journey — Aptitude Question
Two speeds on one journey: A man travels the first 60 km at 30 km/h and the next 60 km at 60 km/h. Answer and worked solution on CodeKairo.
- Topic: Time, Speed & Distance
- Section: Quantitative Aptitude
- Difficulty: Medium
- Time target: 60 seconds
Question
A man travels the first 60 km at 30 km/h and the next 60 km at 60 km/h. What is his average speed?
Options
- 36 km/h
- 40 km/h
- 45 km/h
- 50 km/h
Show the answer and the worked solution
Correct answer: B. 40 km/h
Worked solution
- Times: 60/30 = 2 h and 60/60 = 1 h.
- Total = 120 km in 3 h.
- Average = 40 km/h.
Answer: 40 km/h.
The idea
Equal distances again, so the harmonic mean 2 × 30 × 60/90 = 40 applies. The arithmetic mean of 45 is offered as the trap.
Shortcut. Weight each speed by its time: 2 h at 30 and 1 h at 60 give (60 + 60) ÷ 3 = 40 km/h.
Common trap. 45 km/h — the plain mean of 30 and 60; the car spends twice as long at 30 km/h, which pulls the average down to 40.