chance random choice of 10 from 50 contains no overlap w/

[flyingfreedom]

As a reward for signing up a new member for a music club, Alan will receive 10 different CDs from a list of 50 CDs. Alan already owns some of the 50 CDs on the list. What is the probability that a random selection of 10 different CDs from the list will include 4 CDs that Alan already owns?

I don't think I have sufficient information to answer this question. I Mean shouldn't I have some info on how many cds Alan has?
The answer is 4C4 * 46C6 /50C10
C means combination
If anyone could tell me how one arrives at the answer that would be totally awesome

 

[tkhunny]

Re: word problem

"some" isn't very well defined.