For each contributed $ 0.01 (1 cent) you get 1 ticket.
At the beginning of each game, our system takes totally random long number from 0 to 1 (for example 0.8092768295760276), encodes it through md5, and shows it in encoded form in the beginning of the game. (if you do not know what a md5 is - you can read the article on Wikipedia) Then, when the game is finished, the system displays the number, which was encoded properly at the beginning (you can check it online at md5.cz) and multiplies it by the full amount of games (in cents).
For example, at the end of the game total sum is $ 1,000 and $ 1,000 = 100,000 cents ($ 1 = 100 cents), so you will need to multiply the number of 0.8092768295760276 on 100,000 cents (numbers were taken as an example) and obtain the number 80927. In other words, in the game win a person, who has the ticket 80927.
Consequently, larger sum than you cotribute - the more numbers you get, and thus higher chance to get the same number.
That\'s all. The principle of fair play is that we can not know what will be sum at the end of the game, and random number to multiply sum we give at the beginning of the round and therefore even if we strongly wanted this, it would never have been able to make false winner.