1.4 Complementary Events

Venn diagrams can be a useful way of visualising a sample space. Below can be seen which equally-likely outcomes of the roll of a die are square numbers, and which are not.

The event $\textbf{not A}$, often notated as $\overline{\mathbf{A}}$ or $\mathbf{A'}$, is called the $\textbf{complement of }\mathbf{A}$.