A good way of illustrating probabilities is to use so-called Venn-diagrams. In effect this means representing the probability of an event with circles.

Mutually excluding events can be represented by two separate non-overlapping ciecles.

P(A) + P(B) = P(A U B)

Simultanously events can be illustrated by partially overlapping circles. The overlap then represents the instance of both events happening simultanously.