If A can finish a job in 24 hours and B can finish the same job in 18 hours, how long will it take for both to finish the job together?
Answer: A. 10.8 hours
A's rate is 1/24 and B's rate is 1/18. Together, they complete 1/24 + 1/18 = 7/72 of the work in an hour. Therefore, they will finish the job in 72/7 hours, which is approximately 10.8 hours.