- #1

dizzle1518

- 17

- 0

I need help with the following problem:

The urn contains 5 black and 8 red balls. You close your eyes and

remove balls from the urn one by one without replacement. What is

the probability that the last ball is black?

This looks to me like it is a hypergeometric distribution problem. I set it up in the following way: ((5 choose 4)*(8 choose 8))/(13 choose 12). In order for the last ball to be black we have to remove 12 balls such that the remaining 13th one is black. so we have 5 choose 4 orderings of the black balls and 8 choose 8 orderings of the red balls. Since we are taking out a total of 12 balls then there are 13 choose 12 possible orderings or the red and black balls.

Is this correct?

Thanks,

--David