The campus vets club is having a raffle and is selling 2,600 tickets.

The campus vets club is having a raffle and is selling 2,600 tickets. If the people on your floor of the dorm bought 338 of those tickets, what is the probability that someone on your floor will hold the winning ticket? (Enter your answer as a decimal.)I need to understand the set up of the problem. I do not want just the answer I want to be able to do them on my own and not cheat and just get the answer. Thanks