The mean of a thirteen-item data set is 320. Eleven of the items are 300, 320, 199, 175, 325, 520, 156, 225, 326, 421, and 504. The median is 325. Find the remaining two items in the set if it is known that these items have the greatest possible difference.
(Source: Mathematics Teaching in the Middle School, Nov-Dec 1996)
