The Addition Rule for Probability
Aligned to S-CP.B.7 — Common Core State Standards for Mathematics.
What this lesson teaches
The Addition Rule states P(A or B) = P(A) + P(B) − P(A and B). Subtracting the overlap keeps outcomes shared by both events from being counted twice.
Worked example
Draw one card from a deck. P(king) = 4/52, P(heart) = 13/52, and P(king of hearts) = 1/52. So P(king or heart) = 4/52 + 13/52 − 1/52 = 16/52 = 4/13.
Practice questions
- State the Addition Rule for P(A or B).
- If P(A) = 0.5, P(B) = 0.4, and P(A and B) = 0.1, find P(A or B).
- On a die roll, find P(even or greater than 4).
Watch the lesson
Every lesson comes with a video taught in English and Spanish — the same video the QR code in the printed workbook opens.
▶ Watch this lessonEn español
La Regla de la Suma en probabilidad
La Regla de la Suma establece P(A o B) = P(A) + P(B) − P(A y B). Restar la intersección evita que los resultados compartidos por ambos eventos se cuenten dos veces.
Ejemplo: Saca una carta de una baraja. P(rey) = 4/52, P(corazón) = 13/52 y P(rey de corazones) = 1/52. Así, P(rey o corazón) = 4/52 + 13/52 − 1/52 = 16/52 = 4/13.
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