A person X working alone can complete a work in 5 days. A person Y completes the same amount of work in 15 days, and a person Z when working alone can complete the same amount of work in 30 days. All three people work together for 2 days but then X and Y leave. How many more days does Z need to complete the work after X and Y leave?  Pick:
A) 11
B) 12
C) 13
D) 14
E) 15
The fraction of work completed in two days is 2/5 + 2/15 + 2/30 = 18/30   The fraction of work remaining is 1 - 18/30 = 12/30   The number of days required for Z is 12 days.   The answer is 12.
<result>B</result>
A person X working alone can complete a work in 5 days. A person Y completes the same amount of work in 15 days, and a person Z when working alone can complete the same amount of work in 30 days. All three people work together for 2 days but then X and Y leave. How many more days does Z need to complete the work after X and Y leave?