Probability measures how likely events are, from 0 (impossible) to 1 (certain).
Formula
$P(\text{event}) = \frac{\text{favourable outcomes}}{\text{total outcomes}}$
Example: a bag of 2 red and 3 blue balls gives $P(\text{red}) = \tfrac{2}{5} = 0.4$. For combined events, multiply probabilities along a tree diagram.
Remember
- Probability is between 0 and 1.
- All outcomes' probabilities add up to 1.