## Definition An ==Event== is a subset of the sample space — a collection of outcomes to which a probability can be assigned. A simple event contains exactly one outcome, while a compound event contains two or more outcomes. > [!example]- When rolling a fair six-sided die, what is the event "rolling an even number" and its probability? > The sample space is $S = \{1,2,3,4,5,6\}$. The event $E = \{2, 4, 6\}$ contains 3 of the 6 equally likely outcomes, so > $ P(E) = \frac{|E|}{|S|} = \frac{3}{6} = 0.5 $