Two speeds, one round trip — Aptitude Question
Two speeds, one round trip: A man goes to a place at 12 km/h and returns at 8 km/h, taking 10 hours in all. Answer and worked solution on CodeKairo.
- Topic: Time, Speed & Distance
- Section: Quantitative Aptitude
- Difficulty: Medium
- Time target: 90 seconds
Question
A man goes to a place at 12 km/h and returns at 8 km/h, taking 10 hours in all. What is the one-way distance?
Options
- 36 km
- 42 km
- 48 km
- 54 km
Show the answer and the worked solution
Correct answer: C. 48 km
Worked solution
- d/12 + d/8 = 10.
- Common denominator 24: 2d/24 + 3d/24 = 10 → 5d/24 = 10.
- d = 48 km.
Answer: 48 km.
The idea
Add the two leg times and equate to the total. The answer is the one-way distance, so do not double it unless asked.
Shortcut. The round-trip average is 2 × 12 × 8 ÷ 20 = 9.6 km/h, so 10 h cover 96 km and one way is 48 km.
Common trap. Averaging the speeds to 10 km/h gives a 100 km round trip in 10 hours, so 50 km each way; the times add, not the speeds, so the equation is d/12 + d/8 = 5d/24 = 10.