Suppose we have two urns labelledLandRfor left and right. Each urn contains 4 marblesgiving a total of 8 marbles. Four of the marbles are red, and four are green. LetX0be the numberof red marbles in UrnL. A person reaches with one hand into UrnLand the other hand into UrnR, selects a marble at random from each urn, and then switches those two marbles from one urn to theother (so each urn still has 4 marbles). LetX1denote the number of red marbles in urnLafter theswitch. Let