mutually exclusive event

This is the term used to describe events which can’t happen at the same time.

For example, when we throw a dice throwing 6 and throwing 1 are mutually exclusive because they can’t happen at the same time.

In probability, when two events, A and B, are mutually exclusive:

P(A or B) = P(A) + P(B)

For example, the probability of Ysgol y Dref’s hockey team winning its next game is 0.5, and the probability of the game being a draw is 0.3. Therefore, the probability of winning the game or the game being a draw is:

P(win) + P(draw)
= 0.5 + 0.3
= 0.8