A starts, B finishes — Time & Work Aptitude Question
A starts, B finishes: A can do a work in 15 days. He works for 5 days and then B finishes the rest in 12 days. Answer and worked solution on CodeKairo.
- Topic: Time & Work
- Section: Quantitative Aptitude
- Difficulty: Medium
- Time target: 75 seconds
Question
A can do a work in 15 days. He works for 5 days and then B finishes the rest in 12 days. How long would B alone take for the whole work?
Options
- 15 days
- 18 days
- 20 days
- 24 days
Show the answer and the worked solution
Correct answer: B. 18 days
Worked solution
- A does 5/15 = 1/3 of the work.
- B does the remaining 2/3 in 12 days.
- So B alone would take 12 × 3/2 = 18 days.
Answer: 18 days.
The idea
Find the fraction each person completes, then scale the partial time up to the whole. Never add the two given day counts.
Shortcut. A would have needed 10 more days for the rest; B needed 12, so B is 1.2 times as slow: 1.2 × 15 = 18 days.
Common trap. 24 days — doubling B's 12 days as if A had done half the job; A did only a third.