# 11 4 Theoretical Probability Warm Up Problem of

11 -4 Theoretical Probability Warm Up Problem of the Day Lesson Presentation Lesson Quizzes

11 -4 Theoretical Probability Warm Up 1. Two coins are tossed. What is the probability of getting two heads? 1 4 2. Give the probability that the roll of a number cube will show 1 or 4. 1 3 3. Give the expected number of rolls that will result in a 2 if a number cube is rolled 42 times. 7

11 -4 Theoretical Probability Problem of the Day The name of a U. S. state is spelled out with letter tiles. Then the tiles are placed in a bag, and one is picked at random. What state was spelled out if the probability of picking the letter O is 1 ? 2 3 ? 1? 8 3 Ohio; Colorado; Oregon

11 -4 Theoretical Probability SWBAT find theoretical probability of an event.

11 -4 Theoretical Probability Vocabulary theoretical probability equally likely fair

11 -4 Theoretical Probability Theoretical probability is used to find the probability of an event when all the outcomes are equally likely. Equally likely outcomes have the same probability. If each possible outcome of an experiment is equally likely, then the experiment is said to be fair. Experiments involving number cubes and coins are usually assumed to be fair.

11 -4 Theoretical Probability Additional Example 1 A: Finding Theoretical Probability Andy has 20 marbles in a bag. Of these, 9 are clear and 11 are blue. Find the probability of drawing a clear marble from the bag? Write your answer as a fraction, as a decimal, and as a percent. number of ways the event can occur P = total number of equally likely outcomes of clear marbles Write the ratio. P(clear) = number total number of marbles 9 Substitute. = 20 = 0. 45 = 45% Write as a decimal and write as a percent. The theoretical probability of drawing a clear marble is 9 , 0. 45, or 45%. 20

11 -4 Theoretical Probability Additional Example 1 B: Finding Theoretical Probability Find the probability of drawing a blue marble from the bag. number of ways the event can occur P = total number of equally likely outcomes of blue marbles Write the ratio. P(blue) = number total number of marbles = 11 20 Substitute. = 0. 55 = 55% Write as a decimal and write as a percent. The theoretical probability of drawing a clear marble is 11 , 0. 55, or 55%. 20

11 -4 Theoretical Probability Check It Out: Example 1 A Jane has 20 marbles in a bag. Of these 8 are green. Find the probability of drawing a green marble from the bag? Write your answer as a fraction, as a decimal, and as a percent. number of ways the event can occur P = total number of equally likely outcomes of green marbles Write the ratio. P(green) = number total number of marbles 8 Substitute. = 20 = 0. 4 = 40% Write as a decimal and write as a percent. The theoretical probability of drawing a green marble is 8 , 0. 4, or 40%. 20

11 -4 Theoretical Probability Check It Out: Example 1 B Find the probability of rolling a number more than 4 on a fair number cube. For a fair number cube, each of the six possible outcomes is equally likely. There are 2 ways to roll a number greater than 4: 5 or 6. P= number of ways the event can occur total number of equally likely outcomes P(number more than 4) = 2 numbers more than 4 6 possible outcomes = 2 6 = 1 3 0. 33 33% The theoretical probability of rolling a number more than 4 is 1 , 0. 33, or 33%. 3

11 -4 Theoretical Probability Additional Example 2 A: School Application There are 13 boys and 10 girls on the track team. The name of each of the team members is written on an index card. A card is drawn at random to choose a student to run a sprint and the card is replaced in the stack. Find theoretical probability of drawing a boy’s name. P(boy) = number of boys on the team number of members on the team P(boy)= 13 23 Substitute.

11 -4 Theoretical Probability Remember! The sum of the probabilities of an event and its complement is 1.

11 -4 Theoretical Probability Additional Example 2 B: School Application There are 13 boys and 10 girls on the track team. The name of each of the team members is written on an index card. A card is drawn at random to choose a student to run a sprint and the card is replaced in the stack. Find theoretical probability of drawing a girl’s name. P(boy) + P(girl) = 1 13 23 + P(girl) = 1 - 13 = - 13 23 23 10 P(girl) = 23 13 Substitute 23 for P(boy). 13 Subtract 23 from both sides Simplify.

11 -4 Theoretical Probability Check It Out: Example 2 A A teacher has written the name of each student on a piece of paper and placed the names in a box. She randomly draws a paper from the box to determine which student will present the answer to the problem of the day. If there are 15 boys and 12 girls in the class, what is theoretical probability that a girl’s name will be drawn? Find the number of girls in the class P(girl) = theoretical number of students in the class probability. 12 Substitute. = 27

11 -4 Theoretical Probability Check It Out: Example 2 B What is theoretical probability that a boy’s name will be drawn? P(girl) + P(boy) = 1 12 27 + P(boy) = 1 - 12 = - 12 27 27 15 P(boy) = 27 12 Substitute 27 for P(girl). 12 Subtract 27 from both sides Simplify.

11 -4 Theoretical Probability Lesson Quizzes Standard Lesson Quiz for Student Response Systems

11 -4 Theoretical Probability Lesson Quiz Find the probabilities. Write your answer as a fraction, as a decimal to the nearest hundredth, and as a percent to the nearest whole percent. You have 11 cards, each with one of the letters from the word mathematics. 1. Find the probability of drawing an m from the pile 2 , 0. 18, 18% of shuffled cards. 11 4 , 0. 36, 36% 2. Find the probability of drawing a vowel. 11 3. Find the probability of drawing a consonant. 7 , 0. 64, 64% 11

11 -4 Theoretical Probability Lesson Quiz for Student Response Systems 1. A number cube is rolled. Identify the probability of getting a number less than 4 as a fraction, as a decimal to the nearest hundredth, and as a percent to the nearest whole percent. A. B. C. D.

11 -4 Theoretical Probability Lesson Quiz for Student Response Systems 2. There are 40 balls in a bag. Of these 8 are white, 7 are blue, 12 are green, and 13 are yellow. Identify the probability of drawing a white ball as a fraction, as a decimal to the nearest hundredth, and as a percent to the nearest whole percent. A. B. C. D.

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