Chapter 11 L11-1 Notes: Theoretical Probability

Vocabulary Outcomes—Possible results of a probability event. For example, 4 is an outcome when a number cube is rolled. Event—A specific outcome or type of outcome. Theoretical Probability—The ratio of the number of ways an event can occur to the number of possible outcomes.

Example There are eight equally likely outcomes on the spinner. 1. Find the P(red) 2. Find the P(blue or yellow) 0.25, or 25%.

On Your Own… A counter is randomly chosen. Find each probability. Write each answer as a fraction, a decimal, and a percent. 1. P(4) 2. P(less than 8) 3. P(not a 6)

Vocabulary Complementary Events—Two events in which either one or the other must take place, but they cannot both happen at the same time. The sum of their probabilities is 1.

Example The morning newspaper reported a 20% chance of snow. What is the probability that it will not snow?

Chapter 11 L11-2 Notes: Outcomes

Vocabulary The set of all possible outcomes is called the sample space. A tree diagram is a diagram that shows all possible outcomes of an event.

Example How many outfits are possible from a choice of jean or khaki shorts and a choice of a yellow, white, or blue shirt?

Probability When you know the number of outcomes, you can easily find the probability that an event will occur.

Example Lexi spins two spinners. What is the probability of spinning red on the first spinner and blue on the second spinner?

On Your Own… 1.Use a tree diagram to find how many different words can be made using the words quick, slow, and sad and the suffixes -ness, -er, and -ly. 2.A penny is tossed, and a number cube is rolled. Use a tree diagram to find the probability of getting heads and a 5.

Example The names of three bulldog puppies are shown. In how many different ways can a person choose two of the three puppies? List all of the ways two puppies can be chosen. From the list count only the different arrangements. In this case, AB is the same as BA. There are 3 ways to choose two of the puppies.

On Your Own… 3. How many different ways can a person choose three out of four puppies?