A person X working alone can complete a work in 6 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? Choose the correct option:
A) 12
B) 13
C) 14
D) 15
E) 16
The fraction of work completed in two days is 2/6 + 2/15 + 2/30 = 16/30   The fraction of work remaining is 1 - 16/30 = 14/30   The number of days required for Z is 14 days.   The answer is 14.
<result>C</result>
A person X working alone can complete a work in 6 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?