A can do a piece of work in 20 days. B in 15 days A and C in 12 days. In how many days can A finish the work if he is assisted by B on one day and C on the next, alternately?
Select the correct option:
A) 2 days  B) 5 days  C) 8 days  D) 7 days  E) 9 days
8 days   8 days   A + B = 1/20 + 1/15 = 7/60   A + 8 days = 1/20 + 1/12 = 8/60   7/60 + 8/60 = 15/60 = 1/4   4 days * 2 = 8 days
<result>C</result>
A can do a piece of work in 20 days. B in 15 days A and C in 12 days. In how many days can A finish the work if he is assisted by B on one day and C on the next, alternately?