4.3 Introduction to Probability

The main concepts you need to grasp from this section are the basics of probability and the complement rule. Make sure you understand these key ideas 🔐!

A probability model is a description of some chance process that is made up of two portions: a list of all possible outcomes and the probability for each outcome. The list of all possible outcomes is called a sample space.

📝Basic Probability Rules 

1. If all outcomes in a sample space are equally likely, the probability that event A occurs is...

   1. P(A) = number of outcomes in event A/ total number of outcomes in the sample space.

2. The probability of any event is a number between 0 and 1 (proportion).

3. All possible outcomes MUST add up to 1. 

4. The probability that an event does not occur is 1 minus the probability that it does occur. In other words, this refers to the complement rule which says that P(AC) = 1- P(A) where P(AC) is the complement of event A or the probability that event A doesn’t occur. (*Understand how to solve problems using this rule given a scenario mentioning “at least one.”)

Be sure to know how to interpret the probability you calculate. Remember to use context.

🎥Watch: AP Stats - Probability Rules and Random Variables

Resources:

Courtesy of Make-a-Meme