3. A certain small town, whose population consists of 100 families, has 30 families with 1 child, 50 families with children, and 20 families with 3 children. The birth rank: of one of these children is 1 if the child is the firstborn; 2 if the child is the secondborn, and 3 if the child is the thirdborn. A random family is chosen (with equal probabilities) , and then random child within that family is chosen (with equal probabilities) (Find the PMF pts) , CDF (4 pts) , and mean pts) of a 1.V. X that is defined as the child s birth rank