Probability VOCAB!

What is probability? The probability of an event is a measure of the likelihood that the event will occur. When all outcomes are equally likely, the probability is found as follows: Probability of an event = Number of favorable outcomes Number of possible outcomes Probability RULE: The SUM of the probability of something happening and its complement (not happening) is always 1. P= 0 Impossible P= 1 Certain P= ½ Likely to occur half of the time P= ¼ Unlikely P= ¾ Likely

What is an outcome? A possible result of an experiment. “What happens.” What is an event? A collection of outcomes. What are favorable outcomes? Once you specify an event, the outcomes for that event are called, favorable outcomes. “What I want to have happen- the result I prefer.” What are total possible different outcomes? The sum of all the different possible things that could happen. What is a complement? How likely it is that what I want will not happen.

There are two types of Probability! Theoretical Probability The number of possible favorable outcomes compared to the total possible outcomes; Represented as a fraction, decimal or percent. Experimental Probability The number of favorable outcomes compared to the number of total outcomes from multiple events.

Sample Space all the possible outcomes of an experiment Example: choosing a card from a deck There are 52 cards in a deck (not including Jokers) So the Sample Space is all 52 possible cards: {Ace of Hearts, 2 of Hearts, etc... }

Tossing a Coin When a coin is tossed, there are two possible outcomes: – heads (H) or – tails (T) We say that the probability of the coin landing H is ½. And the probability of the coin landing T is ½. Mathisfun.com

Throwing Dice When a single die is thrown, there are six possible outcomes: 1, 2, 3, 4, 5, 6. The probability of any one of them is 1/6. Mathisfun.com

Example: the chances of rolling a "4" with a die Number of ways it can happen: 1 (there is only 1 face with a "4" on it) Total number of outcomes: 6 (there are 6 faces altogether) So the probability = 1 6 Mathisfun.com

Example: there are 5 marbles in a bag: 4 are blue, and 1 is red. What is the probability that a blue marble will be picked? Number of ways it can happen: 4 (there are 4 blues) Total number of outcomes: 5 (there are 5 marbles in total) So the probability = 4/5 which is equal to 0.8

Mitsu will be randomly assigned to a seat on an airplane. There are a total of 50 seats on the plane. Of these seats, 16 are aisle seats, and the rest are window seats. What decimal represents the probability that Mitsu will be assigned to a window seat? STAAR Question #30

Example A die is thrown once. What is the probability that the score is a factor of 6?