Crossing a bridge on foot — Aptitude Question
Crossing a bridge on foot: A man walking at 5 km/h crosses a bridge in 15 minutes. What is the length of the bridge? Answer and worked solution on CodeKairo.
- Topic: Time, Speed & Distance
- Section: Quantitative Aptitude
- Difficulty: Easy
- Time target: 50 seconds
Question
A man walking at 5 km/h crosses a bridge in 15 minutes. What is the length of the bridge?
Options
- 1,000 m
- 1,250 m
- 1,500 m
- 2,000 m
Show the answer and the worked solution
Correct answer: B. 1,250 m
Worked solution
- Distance = 5 × (15/60) = 1.25 km.
- In metres that is 1,250 m.
Answer: 1,250 m.
The idea
Compute in kilometres, then convert once at the end. Converting the speed to m/min first also works: 5 km/h is 83⅓ m/min.
Shortcut. A quarter of an hour at 5 km/h is a quarter of 5,000 m: 1,250 m.
Common trap. 1,000 m is where writing 15 minutes as 0.15 h leads: 5 × 0.15 = 0.75 km, or 750 m, and 1,000 m is the nearest option. 15 minutes is 0.25 h, so the bridge is 5 × 0.25 = 1.25 km = 1,250 m.