Statistics & Probability

Conditional probability

The probability of one event given that another has occurred. Written P(A | B).

Definition

P(A | B) = P(A and B) ÷ P(B). In tree diagrams without replacement, conditional probabilities appear on the second branch.

Example

Two cards drawn from a pack without replacement. P(2nd card is a heart | 1st was a heart) = 12/51.

Used in these topics

Related terms

Independent events

Events where one occurring does not change the probability of the other. P(A and B) = P(A) × P(B).

Tree diagram

A branching diagram showing all possible outcomes of two or more events and their probabilities.

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