Probability of an Event

For a random experiment whose outcomes are equally likely, the probability of an event $A$ is defined as $P(A) = \frac{n(A)}{n(S)}$ where $n(A)$ is the number of outcomes favourable to $A$ (the outcomes belonging to the subset $A$) and $n(S)$ is the total number of outcomes in the sample space. This single formula - favourable outcomes divided by total outcomes - is the working tool used throughout the rest of the chapter to compute proba …