A person X working alone can complete a work in 6 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 option
A) 9  B) 10  C) 11  D) 12  E) 13
The fraction of work completed in two days is 2/6 + 2/10 + 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>D</result>
A person X working alone can complete a work in 6 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?