P is able to do a piece of work in 15 days and Q can do the same work in 20 days. If they can work together for 4 days, what is t…

Question

P is able to do a piece of work in 15 days and Q can do the same work in 20 days. If they can work together for 4 days, what is the fraction of work left?

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

Correct Answer

Option A — 8/15

Detailed Solution & Explanation

The correct answer is 8/15.

Key Points

• P's rate = 1/15 work/day.
• Q's rate = 1/20 work/day.
• Together per day = 1/15 + 1/20 = 4/60 + 3/60 = 7/60. In 4 days = 4 × 7/60 = 28/60 = 7/15. Work remaining = 1 − 7/15 = 8/15.