8 balls are in a box. Each ball can be either blue or red. If there are d red balls in the box, calculate the probability p(d) that two randomly selected balls from the ball are both blue. Sketch p(d). p(d) = (8-d)/8 * (7-d)/7 = (d^2 - 15d + 56)/56 Now suppose that the box contains 8 balls whereof d red balls and 8-d blue balls. Let Z be the number of red balls when two balls are selected randomly from a box. Find the probability function for Z, end determine E(Z) and Var(Z). Is my thinking correct? Is there an easier way to write this?