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Unformatted text preview: Recap for Confidence Interval for the Mean (Known)A confidence interval is a range of values that has a prespecified probability of including the true value of the parameter. Therefore, a confidence interval for the mean is a range of values that has a prespecified probability of including the mean, . The formula for a confidence interval for the mean when is known is:xz/2/n .The value of /2z(sometimes written as just z) depends on the level of confidence. The higher the level of confidence, the larger the zscore. For example, an 80% confidence interval for the mean is:x1.28n, whereas a 95% confidence interval for is: x1.96n. You should know how to determine the value of /2zfor the desired confidence level.150Example: Genron Corp. would like to determine the mean length of life for the highperformance model of tires that it supplies to an American automobile manufacturer. Forty tires are randomly selected from the manufacturing process and subjected to accelerated lifetesting. The mean from the sample is 33,127 miles. Assume that the standard deviation for the population of tires (that is, ) is 7,500 miles....
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 Fall '09
 Rollins

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