If A can finish a job in 24 hours and B can finish the same job in 36 hours, how long will it take for them to finish the job if they work together?
Answer: A. 14.4 hours
A's rate is 1/24 and B's is 1/36. Together, they complete 1/24 + 1/36 = 5/72 of the work per hour. Therefore, they will finish the job in 72/5 = 14.4 hours.