Length of the platform — Aptitude Question
Length of the platform: A train 120 m long travelling at 54 km/h crosses a platform in 20 seconds. Answer and worked solution on CodeKairo.
- Topic: Time, Speed & Distance
- Section: Quantitative Aptitude
- Difficulty: Medium
- Time target: 60 seconds
Question
A train 120 m long travelling at 54 km/h crosses a platform in 20 seconds. What is the length of the platform?
Options
- 150 m
- 180 m
- 200 m
- 220 m
Show the answer and the worked solution
Correct answer: B. 180 m
Worked solution
- Speed = 54 × 5/18 = 15 m/s; distance in 20 s = 300 m.
- Platform = 300 − 120 = 180 m.
Answer: 180 m.
The idea
Total distance covered minus the train's own length gives the platform. Forgetting to subtract gives 300, which is why the arithmetic must be laid out.
Shortcut. In one line: 54 × 5/18 × 20 = 300 m of train plus platform; strip off the 120 m train to leave 180 m.
Common trap. 150 m — converting 54 km/h by dividing by 4 instead of 3.6 (13.5 m/s), which gives 270 m in 20 s and 270 − 120 = 150.