Making up lost time — Aptitude Question
Making up lost time: A man covers two-thirds of a 120 km journey at 20 km/h. At what speed must he cover the rest… Answer and worked solution on CodeKairo.
- Topic: Time, Speed & Distance
- Section: Quantitative Aptitude
- Difficulty: Medium
- Time target: 90 seconds
Question
A man covers two-thirds of a 120 km journey at 20 km/h. At what speed must he cover the rest to complete the whole journey in 5 hours?
Options
- 30 km/h
- 35 km/h
- 40 km/h
- 45 km/h
Show the answer and the worked solution
Correct answer: C. 40 km/h
Worked solution
- First stretch: 80 km at 20 km/h = 4 hours.
- Remaining distance = 40 km, remaining time = 5 − 4 = 1 hour.
- Required speed = 40 ÷ 1 = 40 km/h.
Answer: 40 km/h.
The idea
Compute the time already used, subtract it from the time allowed, then divide the remaining distance by the remaining time.
Shortcut. 80 km at 20 km/h uses 4 of the 5 hours, and with one hour left the speed equals the remaining distance: 40 km/h.
Common trap. 30 km/h — dividing the whole 120 km by the 4 hours already used; those hours are spent, and 40 km remain for the single hour left.