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Theoretical Probability
Given all outcomes in the sample space are equally likely to occur, the probability that event A occurs can be found using the formula
Probability (Event) = Number of Favorable Events
Total Possible Events
1. Create a sample space (list or diagram of all possible events)
Example: Create the sample space for flipping a coin 3 times
Organized list:
Example: Create the sample space for DeAndre Jordan shooting 3 free throws
Tree Diagram:
Create the sample space for rolling dice.
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Probability Rules:
1. Probability of single event must be between 0 and 1
2. The sum of the probability of all possible outcomes in a sample space must equal 1
3. Probability an Event does not occur is 1 - P(event). This is called the Complement of the Event.
4. If two events have no outcomes in common then the events are Mutually Exclusive The United States Senate is made up of 54 republicans, 2 independents, and 44 democrats. 2
Two Way Tables
Organize outcomes in the sample space that allows us to easily find the P(A) and P(B)
Example: Among middle school students, 70% like chocolate ice cream, 40% like strawberry ice cream, and 30% like both. What is the probability that a randomly selected student will like only chocolate ice cream?
What is the probability that a student will like only strawberry ice cream? What is the probability that a student will like chocolate or strawberry, but not both? 3
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