SOLUTION: A bag contains 7 red marbles, 9 white marbles, and 9 blue marbles. You draw 5 marbles out at random, without replacement. What is the probability that all the marbles are red? What

(a)  What is the probability that all the marbles are red? 

     You can select 5 red marbles of 7 red marbles in   ways. Therefore the answer is  .


(b)  What is the probability that exactly two of the marbles are red?

     You can select 2 red marbles of 7 red marbles in   ways.  Then you can add any 3 marbles of remaining 9+9 = 18 white and blue marbles.

     You can do it in  ways.  Therefore the answer is    ways.



(c)  What is the probability that none of the marbles are red?

     It means that you select 5 marbles among 18 = 9 + 9 white and blue marbles.

     You can do it in   ways.  Therefore, the answer is  .