Probability measures how likely an event is, from 0 (impossible) to 1 (certain).
Formula
$P(\text{event}) = \frac{\text{number of favourable outcomes}}{\text{total number of outcomes}}$
Example: a bag has 2 red and 3 blue balls (5 in total), so $P(\text{red}) = \tfrac{2}{5} = 0.4$.
Remember
- Probability is between 0 and 1.
- $P = \dfrac{\text{favourable}}{\text{total}}$.