Use the formula:Originally Posted byJon

If the probability of an event is then the probability of that event happening out of times is,

In the problems when they are for at most. You need to add up all the probabilities. For example, at most 3: which means probability of exactly 0 plus probability of exactly 1 plus probability of exactly 2 plus probability of exactly 3.

The same with at least only in the other direction.