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 choice from the following options.
A) 20  B) 10  C) 15  D) 5  E) 7
Time taken by 20 to finish the work = XY/(Y-X)   = 10 x 20 / (20-10)   = 200/10= 
<gadget id="calculator">200/10</gadget>
<output>20</output>
20 days   20nswer: 20
<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 ?