In the full lesson
- General Addition Rule (formula)
- Worked Example (example)
- Avoiding Double-Counting (tip)
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Module 2 · Probability Foundations · Topic 4
Addition Rule
Mutually Exclusive Events. If A and B cannot happen at the same time (mutually exclusive), then P(A ∩ B) = 0, and the formula simplifies to P(A ∪ B) = P(A) + P(B).
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Key formulas
From the Probability Foundations formula sheet
- Conditional Probability:
P(A | B) = P(A and B) / P(B)- Probability of A after restricting attention to cases where B occurred. - Bayes' Theorem:
P(A | B) = P(B | A)P(A) / P(B)- Updates a prior probability after observing evidence.
Related glossary terms
- Independence: Two events are independent when one occurring does not change the probability of the other. Example: Two separate fair coin flips are independent.
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