Pre-Algebra 9-1 Probability Warm Up Write each fraction in simplest form Pre-Algebra 9-1 Probability

Pre-Algebra 9-1 Probability Learn to find the probability of an event by using the definition of probability.

Pre-Algebra 9-1 Probability Vocabulary experiment trial outcome sample space event probability impossible certain

Pre-Algebra 9-1 Probability An experiment is an activity in which results are observed. Each observation is called a trial, and each result is called an outcome. The sample space is the set of all possible outcomes of an experiment. ExperimentSample Space  flipping a coin  heads, tails  rolling a number cube  1, 2, 3, 4, 5, 6  guessing the number of  whole numbers jelly beans in a jar

Pre-Algebra 9-1 Probability An event is any set of one or more outcomes. The probability of an event, written P(event), is a number from 0 (or 0%) to 1 (or 100%) that tells you how likely the event is to happen. A probability of 0 means the event is impossible, or can never happen. A probability of 1 means the event is certain, or has to happen. The probabilities of all the outcomes in the sample space add up to 1.

Pre-Algebra 9-1 Probability % 25% 50% 75% 100% NeverHappens about Always happenshalf the timehappens

Pre-Algebra 9-1 Probability Give the probability for each outcome. Example 1A: Finding Probabilities of Outcomes in a Sample Space A. The basketball team has a 70% chance of winning. The probability of winning is P(win) = 70% = 0.7. The probabilities must add to 1, so the probability of not winning is P(lose) = 1 – 0.7 = 0.3, or 30%.

Pre-Algebra 9-1 Probability Give the probability for each outcome. Example 1B: Finding Probabilities of Outcomes in a Sample Space B. Three of the eight sections of the spinner are labeled 1, so a reasonable estimate of the probability that the spinner will land on 1 is P(1) =. 3 8

Pre-Algebra 9-1 Probability Example 1B Continued Three of the eight sections of the spinner are labeled 2, so a reasonable estimate of the probability that the spinner will land on 2 is P(2) =. 3 8 Two of the eight sections of the spinner are labeled 3, so a reasonable estimate of the probability that the spinner will land on 3 is P(3) = = Check The probabilities of all the outcomes must add to = 1

Pre-Algebra 9-1 Probability Give the probability for each outcome. Example 2A A. The polo team has a 50% chance of winning. The probability of winning is P(win) = 50% = 0.5. The probabilities must add to 1, so the probability of not winning is P(lose) = 1 – 0.5 = 0.5, or 50%.

Pre-Algebra 9-1 Probability Give the probability for each outcome. Example 2B B. Rolling a number cube. One of the six sides of a cube is labeled 1, so a reasonable estimate of the probability that the spinner will land on 1 is P(1) =. 1 6 Outcome Probability One of the six sides of a cube is labeled 2, so a reasonable estimate of the probability that the spinner will land on 2 is P(2) =. 1 6

Pre-Algebra 9-1 Probability Example 2B Continued One of the six sides of a cube is labeled 3, so a reasonable estimate of the probability that the spinner will land on 3 is P(3) =. 1 6 One of the six sides of a cube is labeled 4, so a reasonable estimate of the probability that the spinner will land on 4 is P(4) =. 1 6 One of the six sides of a cube is labeled 5, so a reasonable estimate of the probability that the spinner will land on 5 is P(5) =. 1 6

Pre-Algebra 9-1 Probability Example 2B Continued One of the six sides of a cube is labeled 6, so a reasonable estimate of the probability that the spinner will land on 6 is P(6) =. 1 6 Check The probabilities of all the outcomes must add to =

Pre-Algebra 9-1 Probability To find the probability of an event, add the probabilities of all the outcomes included in the event.