# 9 in the previous question the mean finish time is

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9. In the previous question, the mean finish time is 2.164 hours and the standard deviation is 0.85 hours. The distribution is skewed right. What are the mean, standard deviation, and shape of the distribution of z -scores of the same data? (a) Mean = 2.164, Standard deviation = 0.85, skewed right (b) Mean = 2.164, Standard deviation = 0.85, skewed left (c) Mean = 2.164, Standard deviation = 0.85, approximately normal (d) Mean = 0, Standard deviation = 1, skewed right (e) Mean = 0, Standard deviation = 1, approximately normal 2.40 2.35 2.30 2.25 2.20 2.15 2.10 1.0 0.8 0.6 0.4 0.2 0.0 Finish time (hours) Cumulative relative frequency
10. Kitchen appliances don’t last forever. The lifespan of all microwave oven s sold in the United States is approximately Normally distributed with a mean of 9 years and a standard deviation of 2.5 years. What percentage of the ovens last more than 10 years?
82 The Practice of Statistics, 4/e- Chapter 2 © 2011 BFW Publishers Part 2: Free Response Show all your work. Indicate clearly the methods you use, because you will be graded on the correctness of your methods as well as on the accuracy and completeness of your results and explanations. Lamar is shopping for a used car, and he’s interes ted in determining the typical mileage on cars that are three or four years old. He looks at an online car-buying site and compares the number of miles on 30 cars that are three years old to 30 cars that are four years old. His results are summarized by Minitab below. All values are in thousands of miles. Descriptive Statistics: Mileage on Four year old cars and Three year old cars Variable N Mean StDev Minimum Q1 Median Q3 Four year old cars 30 56.68 17.82 23.60 47.80 54.70 64.50 Three year old cars 30 33.33 12.70 14.10 22.33 32.10 39.23 Both distributions are approximately Normally distributed. 11. One car that Lamar is interested in is four years old and has been driven 40 thousand miles. Another one is three years old and has 30 thousand miles on it. How does the number of miles on these cars compare, relative to other cars of the same age? Provide appropriate statistical calculations to support your answer. 12 Based on the information above, estimate the number of four year old cars Lamar looked at that had been driven more than 42 thousand miles. 13. Estimate the 60 th percentile for mileage on the cars Lamar found that were four years old. Maximum 100.30 66.40
© 2011 BFW Publishers The Practice of Statistics, 4/e- Chapter 2 83 14. A researcher wishes to calculate the average height of patients suffering from a particular disease. From patient records, the mean was computed to be 156 cm, with a standard deviation of 5 cm. Further investigation reveals that the scale was misaligned, and that all readings are 2 cm too large, for example, a patient whose height is really 180 cm was measured as 182 cm. Furthermore, the researcher would like to work with statistics based on meters (1 meter = 100 centimeters). What would be the revised values for the mean and standard deviation of the patients’ heights?