Dividing into even groups
I took an intro to probability class last semester and the first week of the intermediate class is a little review. I don't remember too much so can someone confirm to see if this is right?
There are nine indistinguishable items and they are to be divided evenly among three assembly lines.
(A) How many ways can this be done?
My answer is (9 C 3) * (6 C 3) * (3 C 3). There are nine items for the first assembly line, for which you choose 3 for. Then there are six items left for the second line, for which you choose 3. Then three are left for the third.
(B) Two of the items are used and seven are new. What is the probability that a particular line gets both used items?
This one I'm a little unsure about. Any hints?