P(A or B) = P(A) + P(B) - P(A and B) If the events are mutually exclusive P( A and B) = 0 Practice Problem 1: Christmas Ornaments Suppose you were given the following box of Christmas ornaments that contains 14 silver ornaments, 12 red ornament, and 8 green ornaments, What is the probability of randomly choosing a red or green ornament from the box? Step 1: List the events. Event A Event B Step 2: Decide if the events are mutually exclusive or not. The events mutually exclusive because one solid colored ornament be red and green at the same time. Step 3: Write the correct equation and solve for the probability. The events are mutually exclusive, so we should use the equation because P( A and B) - 0. How many total ornaments are In the box? 14 silver ornaments + red ornaments + 8 green ornaments = ornaments. P(R or G) = P(R) + P(G) P( R or G) = + P( R or G) = 24 P(R or G) = This means that out of every 17 ornaments in the box Is a red or green ornament