red_pe_ch_10.pdf

# Describe the likelihood of the event given its

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Describe the likelihood of the event given its probability. 1. The probability that you land a jump on a snowboard is 1 2 . 2. There is a 100% chance that the temperature will be less than 120 ° F tomorrow. Probability The probability of an event is a number that measures the likelihood that the event will occur. Probabilities are between 0 and 1, including 0 and 1. The diagram relates likelihoods (above the diagram) and probabilities (below the diagram). Study Tip Probabilities can be written as fractions, decimals, or percents. Exercises 6 –9 Finding the Probability of an Event When all possible outcomes are equally likely, the probability of an event is the ratio of the number of favorable outcomes to the number of possible outcomes. The probability of an event is written as P (event). P (event) = number of favorable outcomes ——— number of possible outcomes 80% chance Impossible Certain Likely Equally likely to happen or not happen Unlikely 0 1 0 1 0.75 0.5 1 2 0.25 0% 100% 75% 50% 25% 1 4 3 4

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Section 10.2 Probability 409 EXAMPLE Finding a Probability 2 You roll the number cube. What is the probability of rolling an odd number? P (event) = number of favorable outcomes ——— number of possible outcomes P (odd) = 3 6 = 1 2 Simplify. The probability of rolling an odd number is 1 2 , or 50%. There are 3 odd numbers (1, 3, and 5). There is a total of 6 numbers. EXAMPLE Using a Probability 3 The probability that you randomly draw a short straw from a group of 40 straws is 3 20 . How many are short straws? A 4 B 6 C 15 D 34 P (short) = number of short straws —— total number of straws 3 20 = n 40 Substitute. Let n be the number of short straws. 6 = n Solve for n . There are 6 short straws. So, the correct answer is B . 3. In Example 2, what is the probability of rolling a number greater than 2? 4. In Example 2, what is the probability of rolling a 7? 5. The probability that you randomly draw a short straw from a group of 75 straws is 1 15 . How many are short straws? Exercises 11–15
Exercises 10.2 410 Chapter 10 Probability and Statistics Help with Homework 1. VOCABULARY Explain how to find the probability of an event. 2. REASONING Can the probability of an event be 1.5? Explain. 3. OPEN-ENDED Give a real-life example of an event that is impossible. Give a real-life example of an event that is certain. 9 +(-6)=3 3 +(-3)= 4 +(-9)= 9 +(-1)= You are playing a game using the spinners shown. 4. You want to move down. On which spinner are you more likely to spin “Down”? Explain. 5. You want to move forward. Which spinner would you spin? Explain. Describe the likelihood of the event given its probability. 6. Your soccer team wins 3 4 of the time. 7. There is a 0% chance that you will grow 12 more feet. 8. The probability that the sun rises tomorrow is 1. 9. It rains on 1 5 of the days in July. 10. VIOLIN You have a 50% chance of playing the correct note on a violin. Describe the likelihood of playing the correct note.

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