Addition of Probabilities
🎯 Big Idea
When we want to find the probability that at least one of two (or more) events occurs, we use the Addition Rule of Probability. The key word is "OR" — what's the probability of event A or event B happening?
📌 Key Definitions
- Sample Space ($S$): The set of all possible outcomes of an experiment.
- Event: A subset of the sample space — a collection of outcomes we care about.
- Mutually Exclusive Events: Two events that cannot happen at the same time. If $A$ happens, $B$ cannot happen, and vice versa. We say $A \cap B = \emptyset$.
- Non-Mutually Exclusive Events: Two events that can happen at the same time. They share common outcomes, so $A \cap B \neq \emptyset$.