Suppose that two students named Gwyneth and Josephine have a
total of 20 CDs in their room, consisting of 5 blues CDs and 15 reggae CDs. Each of the
students chooses 7 CDs at random (without replacement), with all choices equally likely.
(Thus, altogether, 6 CDs remain unchosen.) Let X denote the number of blues CDs that
Gwyneth selects. Let Y denote the number of blues that Josephine select. find thecovariance between x and y