# Probability of an Event

$$\frac{\text{number of }}{\text{total number of possibilities}}$$

## Example

To calculate the probability that an event occurs:

1. Count the number possibilities that correspond to the event
2. Count the number of possibilities in total
$$P \left( \text{event} \right) = \frac{\text{number possibilities that correspond to the event}}{\text{number of possibilities in total}}$$