The problem first gives conditions: given that an urn contains n orange balls and n yellow balls, and two are selected at random. The question was to determine the probability of getting two balls of different colors. I did (1)*(n)/(2n-1) Where 1 represented the probability of getting either color and the other term represented getting a ball of different color. Anyway the answer was right but the book explained it in a way that i didn't understand. They said that there are n^2 chances of getting orange and then yellow and n^2 chances of getting yellow then orange. They divided this by the total possilbe which was 2n(2n-1) [n^2+n^2]/2n(2n-1) Can someone explain to me why n^2 equals what it equals. Thank you.