A and B together can do a piece of work in 10 days. B alone can finish it in 20 days. In how many days can A alone finish the work ?  Choose the correct option
A) 20 days B) 10 days C) 30 days D) 40 days E) 50 days
20 days   20 days   Time taken by 20 days to finish the work = XY/(Y-X)   10 x 20 / (20-10)   200/10   20 days
<result>A</result>
A and B together can do a piece of work in 10 days. B alone can finish it in 20 days. In how many days can A alone finish the work ?