X and Y can do a piece of work in 20 days and 12 days respectively. X started the work alone and then after 4 days Y joined him till the completion of the work. How long did the work last? Choose the most appropriate option:
A) 5 days B) 10 days C) 11 days D) 20 days E) 25 days
Work done by X in 4 days =1/20	x 4 = 1/5   Remaining work = (1 -1/5) = 4/5   (X + Y)'s 1 day's work = 1/20+1/12 = 8/60 = 2/15   Now,	2/15 work is done by X and Y in 1 day.   So,4/5work will be done by X and Y in	15/2	x 4/5= 6 days.   Hence, total time taken = (6 + 4)= 
<gadget id="calculator">(6 + 4)</gadget>
<output>10</output>
10 days.   ANSWER:10 days
<result>B</result>
X and Y can do a piece of work in 20 days and 12 days respectively. X started the work alone and then after 4 days Y joined him till the completion of the work. How long did the work last?