Length of wall built — Time & Work Aptitude Question
Length of wall built: If 20 men can build a wall 56 metres long in 6 days, what length can 35 men build in 3 days? Answer and worked solution on CodeKairo.
- Topic: Time & Work
- Section: Quantitative Aptitude
- Difficulty: Medium
- Time target: 90 seconds
Question
If 20 men can build a wall 56 metres long in 6 days, what length can 35 men build in 3 days?
Options
- 42 m
- 49 m
- 56 m
- 63 m
Show the answer and the worked solution
Correct answer: B. 49 m
Worked solution
- 20 × 6 = 120 man-days give 56 m.
- 35 × 3 = 105 man-days.
- Length = 56 × 105/120 = 49 m.
Answer: 49 m.
The idea
Set up the proportion output ∝ man-days. More men but fewer days here nets out to slightly less work, so the answer must be under 56.
Shortcut. Man-days go from 120 to 105, a ratio of 7/8, so the wall is 56 × 7/8 = 49 m.
Common trap. 56 m — assuming 35 men for half the days cancels out; 35 is 1.75 times 20, not twice, so output falls to 7/8 of 56.