Calculates the probability of the occurrence of an event given the probability of its nonoccurrence (or the reverse).

P(A) = 1 - P(nonA)

For example, the probability of getting at least one ace in two draws from a standard deck is the negation of not getting an ace at all. The latter is 48/52 * 47/51 or 188/221. So, P(at least one ace in 2 draws) = 221/221 - 188/221 or 33/221.