1. The Classical or ‘A Priori’ Definition of Probability If a random experiment can produce n mutually exclusive and equally likely outcomes, and if m out to these outcomes are considered favourable to the occurrence of a certain event A, then the probability of the event A, denoted by P(A), is defined as the ratio m/n.
Symbolically,
we write
m P( A ) = n Number of favourable outcomes = Total number of possible outcomes