A in 10 days, B in 15 — Time & Work Aptitude Question
A in 10 days, B in 15: A can finish a job in 10 days and B in 15 days. Working together, how long do they take? Answer and worked solution on CodeKairo.
- Topic: Time & Work
- Section: Quantitative Aptitude
- Difficulty: Easy
- Time target: 45 seconds
Question
A can finish a job in 10 days and B in 15 days. Working together, how long do they take?
Options
- 5 days
- 6 days
- 7 days
- 8 days
Show the answer and the worked solution
Correct answer: B. 6 days
Worked solution
- Let the work be 30 units. A does 3 units/day, B does 2 units/day.
- Together they do 5 units/day.
- Time = 30 ÷ 5 = 6 days.
Answer: 6 days.
The idea
Take the total work as the LCM of the individual times so every rate is a whole number. This avoids fractions entirely and is the fastest method in this chapter.
Shortcut. For two workers, time together = product ÷ sum: 10 × 15 ÷ 25 = 6 days.
Common trap. 5 days — half of A's 10 days, as if B were as fast as A; B is slower, so the pair need longer than 5.