Using the Addition Rule

It's helpful to see an example of how to use the Addition Rule once you've got a basic understanding of the formula.

In this lesson video I'm going to use a two way table to find probabilities instead of a Venn diagram to organize our information.

Keep in mind the general process for solving probabilities that involve using the addition rule:

1. Identify if the problem requires the use of the addition rule by it's use of the word "OR".

2. Identify if the events are disjoint or not disjoint.

3. Choose the correct formula to use:

        • Use this formula for disjoint events: $$P(A \bigcup B) = P(A) + P(B)$$
        • Use this formula for events that are not disjoint: $$P(A \bigcup B) = P(A) + P(B) - P(A \bigcap B)$$

4. Solve the probability problem. Consider writing your answer as a decimal or percentage if the fraction is large.