### 3.1 Terminology

*A* and *B* are events

*P*(*S*) = 1 where *S* is the sample space

0 â‰¤ *P*(*A*) â‰¤ 1

*P*(*A*|*B*) = $\frac{P\text{(}A\text{AND}B\text{)}}{P\text{(}B\text{)}}$

### 3.2 Independent and Mutually Exclusive Events

If *A* and *B* are independent, *P*(*A* AND *B*) = *P*(*A*)*P*(*B*), *P*(*A*|*B*) = *P*(*A*) and *P*(*B*|*A*) = *P*(*B*).

If *A* and *B* are mutually exclusive, *P*(*A* OR *B*) = *P*(*A*) + *P*(*B*) and *P*(*A* AND *B*) = 0.

### 3.3 Two Basic Rules of Probability

**The multiplication rule:** *P*(*A* AND *B*) = *P*(*A*|*B*)*P*(*B*)

**The addition rule:** *P*(*A* OR *B*) = *P*(*A*) + *P*(*B*) - *P*(*A* AND *B*)