Multiple choice

A and B, working together, can complete a work in d days. Working alone, A takes (8 + d) days and B takes (18 + d) days to complete the same work. A works for 4 days. The remaining work will be completed by B alone, in:

  1. 24 days

  2. 16 days

  3. 18 days

  4. 20 days

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Combined rate: 1/(8+d) + 1/(18+d) = 1/d. Solving gives d = 12. A's rate = 1/20 per day. In 4 days, A completes 4/20 = 1/5 of work. Remaining work = 4/5. B's rate = 1/30 per day. Time for B = (4/5)/(1/30) = 24 days.