I don't remember those rules, which we learned pretty early on. Logic would say that if an event has 1% odds of resulting in something, doing it twice would double the odds of it happening at least once. However, it's obvious that if you do it 100 times, it's not 100% guaranteed to happen.
Indeed, if you flip two coins, you have 75% odds of having at least 1 heads (only 1 in the 4 possible combinations doesn't involve heads). Mathematically speaking, though, I'm not sure what the formula is.
If I remember correctly the topic was called Permutations and Combinations.
Update by which I totally meant Binomial Theory
