Expert: Jack Cheng - 12/11/2006

Question
A jar contains 7 red , 5 blue , 3 green , and 3 white marbles.4 marbles are drawn without replacement. find the following probability :
a. all marbles drawn are red
b. no more than 2 blue marbles are drawn
c. given the first 2 are red, the 3rd is white, probability that the fourth drawn is white or green.

Answer
Hi David,

Probability is expected/possible.

Possible is 7+5+3+3 = 18.

a. one marble all red: 7/18
  two marbles all red: 6/17
  three marbles all red: 5/16
  four marbles all red: 4/15

Now multiply all four of them to get the final probability.

b. I am not sure exactly what this would be. Rather than possibly misleading you, I'll refer you to someone else. Sorry that I can help on this one.

c. Only 15 marbles left on fourth draw, with 2 white and 3 green. Probability: 5/15 or 1/3.

I Hope this helps,
Jack