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Chapter 7 Review. A z-score is: a) The mean of the distribution b) The deviation from the mean divided by the standard deviation c) Always positive d)

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Presentation on theme: "Chapter 7 Review. A z-score is: a) The mean of the distribution b) The deviation from the mean divided by the standard deviation c) Always positive d)"— Presentation transcript:

1 Chapter 7 Review

2 A z-score is: a) The mean of the distribution b) The deviation from the mean divided by the standard deviation c) Always positive d) The standard error

3 The mean score on a certain mathematics aptitude test is 72, with a standard deviation of 8.5. Assume a normal distribution of scores. If a student's z-score on the test is known to have been at the 25 th percentile, what was the student’s actual score?66.267

4 The life of Sunshine Stereo CD players is normally distributed with a mean of 2.3 years and a standard deviation of 0.4 year. What proportion of the players will break during the guarantee period of 2 years?0.2266

5 From the previous question, P(X < 2) = If the store sells 10 of these CD players on a given day, what is the probability that at least 3 of the players will break during the guarantee period of 2 years?

6 Suppose the average score on a national test is 500 with a standard deviation of 100. If each score is increased by 25%, what are the new mean and standard deviation?  = 625 &  = 125

7 The mean score on a certain mathematics test is 72 with a standard deviation of 8.5. Assume a normal distribution of scores. What score would one have to earn so that no more than 15% of the scores would be higher?80.81

8 Suppose you toss a die with 3 red sides, 2 white sides, and 1 blue side. What is the probability that the first toss that lands blue is the 5 th toss?.0804

9 In a recent study it was found that in one town the number of hours that a typical 10- year-old child watches television per week is evenly distributed with a median of 12 hours and a maximum of 15.5 hours. If Gary is a typical 10-year-old in this town, what is the probability that he watches between 9 and 14 hours?0.7143

10 A traffic control engineer has found that the waiting time for a commuter in the Parker Road toll plaza of North Dallas Tollway during rush hour is approximately uniformly distributed with a mean of 8.7 minutes and a range of 5 minutes. What is the probability that the a randomly selected commuter will have to wait more than 10 minutes?0.24

11 Which of the following statements are true? a) The area under a normal curve is always equal to 1, no matter what the mean and standard deviation are. b) The larger the standard deviation of a normal curve, the taller and thinner the curve. c) Normal curves with different means are centered around different numbers. T F T

12 A Cornell University researcher measured the mouth volumes of men and women. She found a mean of 66 cc for men (  = 17 cc) and a mean of 54 cc for women (  = 14.5 cc). If the distribution of mouth volumes is approximately normal, what is the probability that the difference in volumes (male – female) is at least 59 cc?.0179


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