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Confidence Intervals, Sample Size

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In order to determine the fuel efficiency for the Subaru Impreza the following information was gathered:

a) A random sample of 12 Imprezas were driven yielding the following miles per gallon (mpg).

25.1 24.6 22.5 27.8 26.1 21.0 23.9 28.4 24.4 23.5 26.2 20.7

Create a 95% confidence interval estimate for the population mean mpg's for the Subaru Impreza.
b) Later, a larger sample of 100 Imprezas were driven yielding an average of 24.6 mpg's and a standard deviation of 2.8 mpg's. Create a 98% confidence interval estimate for the population mean mpg's for the Subaru Impreza.

c) What is the minimum sample size that would be required to estimate this population's mean to within + or - .05 mpgs with a 90% confidence? (Assume standard deviation = s from part b)

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