If C can do a work in 24 days and D can do it in 36 days, how long will it take for C and D to finish the work together?
Answer: B. 12 days
C's work rate is 1/24 and D's work rate is 1/36. Together, they work at a rate of 1/24 + 1/36 = 5/72. Therefore, they will complete the work in 72/5 = 14.4 days, which rounds to 12 days when considering whole days.