4.3 Introduction to Probability

Part of Probability, Random Variables, and Probability Distributions in AP® Statistics. Read the opening section, then create a free account for the full interactive lesson, practice, and progress tracking.

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Probability Rules

Basic probability rules:

Rule 1: For any event ${A}$ : ${0 \leq P(A) \leq 1}$

Rule 2 (Sample Space Rule): ${P(S) = 1}$ — some outcome always occurs

Rule 3 (Complement Rule):

P(A^c) = 1 - P(A)

where

{A^c}

is the complement of

{A}

(event A does NOT occur)

Rule 4 (Addition Rule for Mutually Exclusive Events): If

{A}

and

{B}

cannot both occur:

P(A \text{ or } B) = P(A) + P(B)

Equally likely outcomes

P(A) = \frac{\text{number of outcomes in A}}{\text{total number of outcomes in S}}

Example: Roll a fair die: ${P(\text{even}) = \frac{3}{6} = 0.5}$

In this unit

12 lessons

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