Probability of winning a drawing/lottery

I can't seem to get my head around this: A random drawing will be held for which there are 900 tickets sold, for which there will be one winning ticket drawn. If you purchased 25 tickets, what is the probability that you will win.

I am pretty sure this follows a binomial distribution, but I don't know how to adopt the models to solve the problem.

Any help / directin would be appreciated. I am looking more to undertsand the problem domain than to get an answer.

This is much simpler than a binomial distribution. If there are $n$ equally likely outcomes, the probability of each is $1/n$, and the probability of a set $S$ of them is $|S|/n$. This tells you the probability the winning ticket will be among those in the set $S$. – Douglas Zare Sep 28 '12 at 14:28