Say that you have a deck of cards that contains O cards. You want to be able to take at least M cards out of a deck that fit a certain criteria (i.e. they need to be aces or they need to be spades). Let's say that there are N such cards that fit the criteria (where N >= M) in the deck.
During a showing of cards, someone takes Z cards from the deck and places them face up. If you see a card that you want during this showing, you will take it into your possession and remove it from the deck. After the showing, the unclaimed cards will be shuffled back into the deck. Any removed cards are permanently gone from the deck for future showings.
If there are Y of these showings of Z cards, what are the odds that you will have at least X cards that fit the criteria at the end?