Assuming that an event has 80% chance of occurrence and 20% of not occurring per "round", what is the formula to calculate the likelihood that it will occur at least n times assuming that there are x rounds? i.e. If you flip a coin 3 times, what are the chances that at least 2 times will turn up heads? This example would be simple enough to map out all of the occurrences and find out which proportion meet those criteria, but the examples i will need to work with are too complex to do so. I tried to find the formula online but didnt know the name and couldnt describe it in such a way that a google search yielded results. Thanks!