4.2 Basic Probability Rules

Give a probability model for a chance process with equally likely outcomes and use it to find the probability of an event.

Use the complement rule to find probabilities.

Use the addition rule for mutually exclusive events to find probabilities.

A probability model is a description of some chance process that consists of two parts: a list of all possible outcomes and the probability for each outcome.

The list of all possible outcomes is called the sample space.

A probability model allows us to find the probability of an event.

An event is any collection of outcomes from some chance process.

The probability of any event is a number between 0 and 1.

All possible outcomes together must have probabilities that add up to 1.

The probability that an event does not occur is 1 minus the probability that the event does occur.

Two events A and B are mutually exclusive if they can not happen at the same time. P(A and B) = 0

The addition rule for mutually exclusive events A and B says that P(A or B) = P(A) + P(B)