A box contains 3 yellow balls and 5 black balls. One by one, every ball is selected at random without replacement. What is the probability that the fourth ball selected is black?	Pick.
A) 1/4  B) 1/2  C) 1/2  D) 5/8  E) 2/3
Let the 5 black balls be BBBBB and 3 Red Balls be RRR   They can be arranged in 8 slots _ _ _ _ _ _ _ _   in (8!)/ (5!x3!)   If the fourth slot is Black ball then the arrangement will be to fill   _ _ _ B _ _ _ _   we have 7 slots and 4 Black (BBBB) and 3 Red (RRR)   They can be arranged in (7!)/ (4!x3!)   Hence required probability = [(7!)/ (4!x3!)] / [(8!)/ (5!x3!)]   Ans = 5/8 5/8
<result>D</result>
A box contains 3 yellow balls and 5 black balls. One by one, every ball is selected at random without replacement. What is the probability that the fourth ball selected is black?