## Essentials of Statistics (5th Edition)

$P(B|A)$ is the probability that if A happens, then B will happen too.
E.g. event A:when choosing a random number, getting an odd one. Event B:when choosing a random number, getting one, that is divisible by 3. Here $P(B|A)$ is the probability that if we get an odd number, we get one that is divisible by 3.