This resource is used to introduce students to mutually exclusive events. Before receiving a definition of this concept, students must determine whether a variety of situations could happen at the same time. Students are then guided through several examples in order to determine the probability of mutually exclusive events (A or B). Two versions of the resource can be used at this point in the activity. In the advanced form (Version A), students work through a card example to find the probability of two non-mutually exclusive events. Students should be able to discover the formula on their own. In the standard form (Version B), students are simply given the formula to find the probability of two non-mutually exclusive events. Both versions include a page of real-world application questions, so students can practice finding probabilities. A key is provided.