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Unformatted text preview: MA 2611 D' 07 Quiz 3a Solution 1. (7 points) A 99% confidence interval for a population mean is (0.51, 2.73). This means that in 99% of all possible samples, the population mean will lie between 0.51 and 2.73. True or false? If false, give a correct interpretation of the confidence level. Solution: False. A correct interpretation is "In 99% of all possible samples from this population, a 99% confidence interval computed using the sample data will contain the population mean ". 2. 20 tires of a new design give tread lives having a sample mean of 42,357 miles and a sample standard deviation of 3,042 miles. The data show no evidence of outliers or nonnormality. (a) (7 points) Obtain a 95% confidence interval for the true mean tread life. ^ ^ Solution: The interval is y (Y )t19,0.975 . Since (Y ) = s/ n = 3042/ 20 = 680.2, and t19,0.975 = 2.093, the interval is 42357 680.2 2.093 = (40933, 43781) (b) (6 points) From this interval can you conclude that population mean tread life exceeds 42,000 miles? Why or why not? Solution: No, since 42,000 lies in the interval, it is a plausible value of , so we can't conclude > 42000. ...
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This homework help was uploaded on 04/09/2008 for the course MA 2611 taught by Professor Petrucelli during the Spring '08 term at WPI.
 Spring '08
 Petrucelli

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