Tango:: Color Tango: S Notes Handout Slide Sorter Example Two refills for a ballpoint pen are selected at random from a box that contains 3 blue refills, 2 red refills and 3 green refills. If X is the number of blue refills and Y is the number of red refills selected, find a. The joint probability mass function p(x, y), and b. P[(X, Y) E A], where A is the region {(x, y)|x + y ≤ 1}