Puneet hires three person X, Y and Z to do a piece of work. They can do the piece of work in 50, 75 and 20 days respectively. They started working together after 4 days Z quits the work. In how many days X and Y take to finish the rest of the work ?

X, Y, Z complete work in 50, 75, 20 days respectively. Their combined rate = 1/50 + 1/75 + 1/20 = 3/150 + 2/150 + 7.5/150 = 12.5/150 per day. In 4 days, they complete 50/150 = 1/3 of work. Remaining work = 2/3. X + Y rate = 1/50 + 1/75 = 5/150 per day. Time for remaining work = (2/3) / (5/150) = 100/5 = 20 days. Options B, C, D are calculation errors.