A is able to complete a task in 15 days, while B takes 20 days to finish the same task. If they collaborate and work together for…

Question

A is able to complete a task in 15 days, while B takes 20 days to finish the same task. If they collaborate and work together for 4 days, what fraction of the work will still remain?

1. A. 1/4
2. B. 7/15
3. C. 8/15 (Correct answer)
4. D. 11/15

Correct Answer

Option C — 8/15

Detailed Solution & Explanation

The correct answer is 8/15.

Key Points

• A's rate = 1/15, B's = 1/20, together = 1/15 + 1/20 = 7/60 per day.
• In 4 days they finish 4 × 7/60 = 28/60 = 7/15. Remaining = 1 − 7/15 = 8/15.
• Add individual one-day rates for the combined rate, multiply by the days worked, then subtract from the whole job.