A box contains 20 red balls, 30 white balls and 50 blue balls. Suppose that 10 balls are selected at random one at a time and let X be the number of colors missing from the 10 selected balls.

a) Determine the probability mass and distribution function of X if the selections are made with replacement.

b) Determine the probability mass and distribution function of X if the selections are made without replacement.

http://www.bilkent.edu.tr/~math250/Solution%20set2.pdf