An event is a subset of the sample space for a random experiment.

For example, the set of outcomes from tossing two coins is { HH,HT,TH,TT }, where H represents a ‘head’ and T a ‘tail’.

For example, if A is the event ‘at least one head is obtained’, then A = { HT,TH, HH }.

Two events A and B are mutually exclusive if one is incompatible with the other; that is, if they cannot be simultaneous outcomes in the same chance experiment.

For example, when a fair coin is tossed twice, the events ‘HH’ and ‘TT’ cannot occur at the same time and are, therefore, mutually exclusive.

In a Venn diagram, as shown below, mutually exclusive events do not overlap.