Meeting on a circular track — Aptitude Question
Meeting on a circular track: Two runners on a 400 m circular track run in the same direction at 5 m/s and 3 m/s. Answer and worked solution on CodeKairo.
- Topic: Time, Speed & Distance
- Section: Quantitative Aptitude
- Difficulty: Medium
- Time target: 75 seconds
Question
Two runners on a 400 m circular track run in the same direction at 5 m/s and 3 m/s. After how long do they first meet again?
Options
- 100 s
- 150 s
- 200 s
- 250 s
Show the answer and the worked solution
Correct answer: C. 200 s
Worked solution
- Relative speed = 5 − 3 = 2 m/s.
- To meet, the faster must gain 400 m.
- Time = 400 ÷ 2 = 200 s.
Answer: 200 s.
The idea
Same direction on a circular track: the gap to close is one full lap at the difference of the speeds. Opposite directions would use the sum.
Shortcut. Back-check: in 200 s the runners cover 1,000 m and 600 m, exactly one 400 m lap apart.
Common trap. Adding the speeds, the rule for runners going opposite ways, gives 400 ÷ 8 = 50 s; running the same way, the faster gains only 5 − 3 = 2 m/s and must gain a whole 400 m lap before they meet.