Explaining probability

[Beck]

I need a little help form you. A non-poker-playing friend of mine was watching me play, when I had a flush draw on the flop. He then said, that I was calculating probalities incorrectly when I stated I would make my flush 9 out of 47 times on the turn (9 of the suit, 47 unseen cards).
he claims that this is incorrect, since I don't know which cards the other players are holding.

But I'm lacking the corrct words to explain it to him. Any ideas?

[uuDevil]

This comes up every so often. See this thread, (http://forumserver.twoplustwo.com/showthreaded.php?Cat=&Number=565745&page=&view=&sb =5&o=&vc=1) especially BruceZ's reponse.