Together, then B alone — Time & Work Aptitude Question
Together, then B alone: A can do a work in 12 days and B in 15 days. They work together for 4 days, after which A… Answer and worked solution on CodeKairo.
- Topic: Time & Work
- Section: Quantitative Aptitude
- Difficulty: Medium
- Time target: 90 seconds
Question
A can do a work in 12 days and B in 15 days. They work together for 4 days, after which A leaves. In how many more days will B finish?
Options
- 5 days
- 6 days
- 7 days
- 8 days
Show the answer and the worked solution
Correct answer: B. 6 days
Worked solution
- Combined rate = 1/12 + 1/15 = 5/60 + 4/60 = 9/60 = 3/20.
- In 4 days: 4 × 3/20 = 3/5 done, so 2/5 remains.
- B needs (2/5) ÷ (1/15) = 6 days.
Answer: 6 days.
The idea
Work done, work remaining, then divide by the rate that continues. The question asks for the extra days, not the total.
Shortcut. A's 4 days cover 4/12 = 1/3 of the job, so B does 2/3 — 10 of his 15 days. He has already worked 4, leaving 6.
Common trap. 5 days — taking the work left as the third that A did (4/12) rather than the 2/5 still undone; 1/3 × 15 = 5.