A bag has r red and b blue balls. Balls are picked at random without replacement. Let

Question:

A bag has r red and b blue balls. Balls are picked at random without replacement. Let X be the number of selections required for the first red ball to be picked.
(a) Explain why X does not have a geometric distribution.
(b) Show that the probability mass function of X is

(r+b – k` r – 1 for k = 1,2, ...,b+1. P(X = k) = (:) т+