Conditional Probability
Aligned to S-CP.B.6 — Common Core State Standards for Mathematics.
What this lesson teaches
The conditional probability P(A | B) is the chance of A given that B has happened. It equals the fraction of B's outcomes that are also in A, computed as P(A and B) divided by P(B).
Worked example
Draw one card from a deck. Find P(King | face card). There are 12 face cards, and all 4 kings are face cards. So among B's outcomes (the 12 face cards), 4 are kings: P(King | face card) = 4/12 = 1/3.
Practice questions
- Roll a die: find P(6 | the roll is even).
- Of 20 students, 8 play sports and 5 of those are seniors: find P(senior | plays sports).
- Explain in words what P(rain | cloudy) means.
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
Probabilidad Condicional
La probabilidad condicional P(A | B) es la posibilidad de A dado que B ya ocurrió. Es igual a la fracción de los resultados de B que también están en A, calculada como P(A y B) dividido entre P(B).
Ejemplo: Saca una carta de una baraja. Encuentra P(Rey | carta de figura). Hay 12 cartas de figura, y los 4 reyes son cartas de figura. Así que entre los resultados de B (las 12 cartas de figura), 4 son reyes: P(Rey | carta de figura) = 4/12 = 1/3.
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