A bag contains 3 blue and 5 white marbles. One by one, marbles are drawn out randomly until only two are left in the bag. What is the probability X that out of the two, one is white and one is blue?
Answers:  A) 15/56  B) 41/56  C) 13/28  D) 15/28  E) 5/14
The required probability X= probability of choosing 6 balls out of the total 8 in such a way that we remove 4 out of 5 white and 2 out of 3 blue balls.   Ways to select 6 out of total 8 = 8C6   Ways to select 4 out of 5 white balls = 5C4   Ways to select 2 out of 3 blue balls = 3C2   Thus the required probability = (5C4*3C2)/8C6 = 15/28.   15/28 is thus the correct answer.
<result>D</result>
A bag contains 3 blue and 5 white marbles. One by one, marbles are drawn out randomly until only two are left in the bag. What is the probability X that out of the two, one is white and one is blue?