A can complete a task in 16 hours, while B can complete the same task in 24 hours. If they work together for 4 hours, how much of the task is completed?
Answer: B. 1/3
A's work rate is 1/16 and B's work rate is 1/24. Together, they complete 1/16 + 1/24 = 5/48 of the task in one hour. In 4 hours, they complete 4 * 5/48 = 20/48 = 5/12 of the task.