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PROBABILITY 6-4 VOCABULARY – possible results of an action. Event – any outcome or group of outcomes. The outcomes are called “favorable outcomes” Probability – equally likely outcomes. Could be expressed in a ratio Outcomes Probability P(event) = number of favorable outcomes number of possible outcomes Ex.) Find P(rolling an even number) with one number cube. # of favorable outcomes = 3 # of possible outcomes 6 P(rolling an even number) = 3/6 or 1/2 Range of Probability All probabilities range from 0 to 1. Most possible answers will be in fraction or decimal form. Probability Less likely 0 IMPOSSIBLE EVENT More likely 0.5 Equally likely as unlikely 1 CERTAIN EVENT COMPLEMENTS A complement of an event is the opposite of that event. The events “rain” and “no rain” are complements of each other, for example. The probability of an event plus the probability of its complement always equal 1. EXAMPLE Find each probability of one roll of a number cube.