Complementary events

 Complementary events are events that cannot happen at the same time, and whose probabilities add up to 1. In other words, the probability of one event occurring is the complement of the probability of the other event occurring.

For example, let's say you are flipping a coin. The complementary events in this case are getting heads or getting tails. If the probability of getting heads is 50%, the probability of getting tails is also 50%. These probabilities add up to 100%, or 1.

Complementary events are often used in probability and statistics to calculate the probability of an event occurring. For example, if you want to know the probability of an event occurring, you can subtract the probability of the complementary event from 1.

For example, let's say you are rolling a die and you want to know the probability of rolling an odd number. The complementary event in this case is rolling an even number. If the probability of rolling an even number is 1/2, the probability of rolling an odd number is 1 - 1/2 = 1/2, or 50%.