A is 30% more efficient than B. How much time will they, working together, take to complete a job which A alone could have done in 23 days?
Answer: B
Let B's efficiency be 10 units/day. Then A's efficiency is 13 units/day. A alone takes 23 days, so total work = \(13 \times 23 = 299\) units. Working together, their efficiency is 10+13 = 23 units/day. Time taken together = Total work / Combined efficiency = 299 / 23 = 13 days.