Teacher presentation materials. Unit: Geo.8 Conditional Probability (Geometry). Geo.8 Conditional Probability In this unit, students extend what they learned about probability in grade 7 by considering events that are combined in various ways including both occurring, at least one occurring, and one event happening under the condition that the other happens as well. This unit introduces the relationship between probabilities of some combinations of events using the Addition Rule, \(P(\text{A or B}) = P(\text{A}) + P(\text{B}) - P(\text{A and B})\) . Conditional probability is discussed. In particular, the Multiplication Rule \(P(\text{A and B}) = P(\text{A | B}) \boldcdot