A person X working alone can complete a work in 5 days. A person Y completes the same amount of work in 10 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 answer.
A) 6
B) 7
C) 8
D) 9
E) 10
The fraction of work completed in two days is 2/5 + 2/10 + 2/30 = 20/30   The fraction of work remaining is 1 - 20/30 = 10/30   The number of days required for Z is 10 days.   The answer is 10.
<result>E</result>
A person X working alone can complete a work in 5 days. A person Y completes the same amount of work in 10 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?