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Unformatted text preview: Re-cap for Confidence Interval for the Mean (Known)A confidence interval is a range of values that has a pre-specified probability of including the true value of the parameter. Therefore, a confidence interval for the mean is a range of values that has a pre-specified 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 z-score. 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 high-performance model of tires that it supplies to an American automobile manufacturer. Forty tires are randomly selected from the manufacturing process and subjected to accelerated life-testing. 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