X is 50% more efficient than Y. If Y can do a work in 30 days, then in how many days can X and Y together do the work?
Answer: B
Let Y's efficiency be 2 units/day. Then X's efficiency is 3 units/day. Y takes 30 days, so total work = \(2 \times 30 = 60\) units. Combined efficiency = 2+3=5 units/day. Time taken together = 60/5 = 12 days.