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Stat 101 – Sheet 8 King Saud University Almajmaa’h Engineering College STAT 101 1430/2009 --------------------------------------------------------------------------------------------------------------------------------------- Sheet (8) Probability 1. Briefly explain the two properties of probability. 2. Briefly describe an impossible event and a sure event. What is the probability of the occurrence of each of these two events? 3. Briefly explain the three approaches to probability. Give one example of each approach. 4. Briefly explain for what kind of experiments we use the classical approach to calculate probabilities of events and for what kind of experiments we use the relative frequency approach. 5. Which of the following values cannot be probabilities of events and why? 1/5 .97 −.55 1.56 5/3 0.0 −2/7 1.0 6. Which of the following values cannot be probabilities of events and why? .46 2/3 −.09 1.42 .96 9/4 −1/4 .02 7. Thirty-two persons have applied for a security guard position with a company. Of them, 7 have previous experience in this area and 25 do not. Suppose one applicant is selected at random. Consider the following two events: This applicant has previous experience, and this applicant does not have previous experience. If you are to find the probabilities of these Dr. SaMeH Page 1 Stat 101 – Sheet 8 two events, would you use the classical approach or the relative frequency approach? Explain why. 8. The president of a company has a hunch that there is a .80 probability that the company will be successful in marketing a new brand of ice cream. Is this a case of classical, relative frequency, or subjective probability? Explain why. 9. The coach of a college football team thinks there is a .75 probability that the team will win the national championship this year. Is this a case of classical, relative frequency, or subjective probability? Explain why. 10. A random sample of 2000 adults showed that 1120 of them have shopped at least once on the Internet. What is the (approximate) probability that a randomly selected adult has shopped on the Internet? 11.In a group of 50 executives, 29 have a type A personality. If one executive is selected at random from this group, what is the probability that this executive has a type A personality? 12. A multiple-choice question on a test has five answers. If Dianne chooses one answer based on “pure guess,” what is the probability that her answer is a. correct? b. wrong? Do these two probabilities add up to 1.0? If yes, why? 13.Suppose you want to find the (approximate) probability that a randomly selected family from Los Angeles earns more than $125,000 a year. How would you find this probability? What procedure would you use? Explain briefly. Dr. SaMeH Page 2