Complementary Events

Complementary Events

Events that do not have any common elements and for which their assembly corresponds to set of all possible of a random experiment.

The expression complementary events is a synonym for contrary events.


The complementary event of an event E is noted as E’.

Therefore, we have E ∪ E’ = Ω.


In the random experiment that consists of rolling a fair die with six faces numbered 1 to 6 and recording the result that appears on the top face, the events “A: getting an even result” and “A’: getting an odd result” are complementary events, because their combination corresponds to the set of possible outcomes, which is: Ω = {1, 2, 3, 4, 5, 6}.

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