A bag contains 10 red marbles and 5 blue marbles. You randomly select 3 marbles from the bag. What is the probability that all 3 marbles are blue when (a) you replace each marble before selecting the next one and (b) you do not replace each marble before selecting the next one?

(a) 1/3 (b) 1/3
(a) 1/27 (b) 1/3
(a) 1/27 (b) 2191
(a) 1/3 (b) 2/91