In an urn containing N balls, a proportion p is white and q = 1 - P are black. A ball is drawn and its color noted. The ball drawn is then replaced, and Nr balls are added of the same color as the ball drawn. The process is, repeated until n balls have been drawn. For j = 1, 2, ... , n let X_j be equal to 1 or 0, depending on whether the ball drawn on thejth draw is white or black. Show that the correlation coefficient between X_i and X_j is equal to r|(l + r).