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Unit 4

4.3 Introduction to Probability

1 min readโ€ขjune 11, 2020

Aly Moosa

Kanya Shah


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 ๐Ÿ”!

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.

๐Ÿ“Basic Probability Rulesย 

  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.ย 

  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 doesnโ€™t occur. (*Understand how to solve problems using this rule given a scenario mentioning โ€œat least one.โ€)

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

๐ŸŽฅWatch: AP Stats - Probability Rules and Random Variables

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2Fmay-the-probability.jpg?alt=media&token=e3fafba5-ea36-4f92-a89a-a34aec9d3f65

Resources:

Courtesy of Make-a-Meme

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