If you are looking at percentage, your math is correct but not for statistical probability, which is a whole different realm of applied mathematics. Assuming all 1000 tickets were sold each ticket maintains a 1 in 1000 chance of winning - that is a constant no matter how many tickets you own. So that gives you 4 chances of 1 in 1000 not 1 in 250.
For statistical probability---4 chances in 1000 IS 1 in 250. Given a pool of 1000 ticket stubs, four of which have your name on them---there is a 1 in 250 chance that a stub with your name on it will be chosen.
Seriously.
Again, look at the dice example. The raffle works exactly the same way, it is merely a larger pool to start with.
If, on a die, you said "I win on a roll of 1, 2, or 3". Each one of those choices has a 1 in 6 chance. Three of them (3 out of 6) gives you a chance to win. Therefore, your chance is 3/6 or 1 in 2---which is 50%. This isn't a surprise, since 1, 2, and 3 are half of the possible sides.
(If you don't like that one, again: you win on a roll of a die with a 1 or a 2 showing up. Each has a 1/6 chance. So your total chance of winning [there being a limited number of choices of results] is 2/6 or 1/3. Which again, makes sense because you win on 1/3 of the possible faces of the die showing up.)
The raffle is the same. If you have 4 tickets, each of which have a 1 in 1000 chance, then you have a 4 in 1000 chance of winning. Out of the possible pool of choices (1000 of them), 4 of them will cause you to win. 4/1000 = 1/250. Probability is 4/1000 = .004 = .4% ---but this is the same as the probability of 1 in 250. (Check the math.
1/250 = .004
This IS statistical probability. There is one draw out of the possible pool. Four chances out of 1000 will cause you to win. And you have a 1/250 chance of winning. You are correct that each ticket only has a 1/1000 chance of winning. However, YOUR chances of winning is the aggregate of each ticket's chances.
