# Conditional Probability

the probability of an event occurring, given that another event has already occurred

## Example

There are 5 marbles in a jar: 2 are blue, 3 are red. You pick a marble randomly. If it is blue, you earn \$2, otherwise you lose \$1.

A blue marble has a black dot on it while the other one does not.

Two of the red marbles are marked with a dot.