Created by Michele Hinkle and Jeffrey Fries March 2005 Probability Created by Michele Hinkle and Jeffrey Fries March 2005

Definitions Event: Something that may or may not happen. Probability: The chance of an event happening. Impossible: An event that can never happen. Certain: An event that must happen.

The Probability Continuum If an event has a probability of ½, some people say that there is a 50-50 chance that the event will happen. unlikely likely impossible 1/2 equally likely 1 certain

Making Predictions: Suppose you flip a coin 20 times Making Predictions: Suppose you flip a coin 20 times. How many times will it land heads up? When you know the probability of an event, you can use this probability to make a prediction.

Since the probability of a coin landing heads up is 1/2, you can predict that if you flip a coin 20 times, it will probably land heads up ½ of 20, or 10 times. There is no guarantee that this will actually happen, but it is a reasonable prediction.

Example: Describe the likelihood of picking a green egg from the bag. Since all the eggs are green, any egg you choose will be green. You are certain to pick a green egg. 4 Number of favorable outcomes 4 Number of possible outcomes

Since no eggs are green, whichever egg you choose will not be green Since no eggs are green, whichever egg you choose will not be green. It is impossible to pick a green egg. Number of favorable outcomes 4 Number of possible outcomes

2 of the 4 eggs, or ½ of the eggs are green 2 of the 4 eggs, or ½ of the eggs are green. You have an equally likely chance of picking a green egg as not picking a green egg. 2 Number of favorable outcomes 4 Number of possible outcomes

It is unlikely, but not impossible, that you will pick a green egg from the bag that has only one green egg. 1 Number of favorable outcomes 4 Number of possible outcomes

It is likely, but not certain, that you will pick a green egg from the bag that has three green eggs. 4 Number of favorable outcomes 5 Number of possible outcomes

The Probability Continuum unlikely likely impossible 1/2 equally likely 1 certain