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Chapter 7 Review

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A z-score is: The mean of the distribution The deviation from the mean divided by the standard deviation Always positive The standard error

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

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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

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**From the previous question, P(X < 2) = 0. 2266**

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? 0.4033

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

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The mean score on a certain mathematics test is 72 with a standard deviation of 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

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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 5th toss? .0804

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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

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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

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**T F T Which of the following statements are true?**

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

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A Cornell University researcher measured the mouth volumes of men and women. She found a mean of 66 cc for men (s = 17 cc) and a mean of 54 cc for women (s = 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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