Working different hours a day — Aptitude Question
Working different hours a day: 39 people can repair a road in 12 days working 5 hours a day. Answer and worked solution on CodeKairo.
- Topic: Time & Work
- Section: Quantitative Aptitude
- Difficulty: Medium
- Time target: 90 seconds
Question
39 people can repair a road in 12 days working 5 hours a day. In how many days will 30 people working 6 hours a day complete it?
Options
- 11 days
- 13 days
- 15 days
- 18 days
Show the answer and the worked solution
Correct answer: B. 13 days
Worked solution
- Total = 39 × 12 × 5 = 2,340 person-hours.
- Daily output of the new team = 30 × 6 = 180 person-hours.
- Days = 2,340 ÷ 180 = 13 days.
Answer: 13 days.
The idea
When hours per day vary, work in person-hours rather than person-days. Everything else is the same chain rule.
Shortcut. Cancel before multiplying: 12 × 39 × 5 ÷ (30 × 6) = 2 × 39 × 5 ÷ 30 = 390 ÷ 30 = 13 days.
Common trap. 15 days — the nearest option to 15.6, which is what ignoring the change from 5-hour to 6-hour days gives (12 × 39 ÷ 30).