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Time required to prepare a federal income tax return

AARP reported on a study conducted to learn how long it takes individuals to prepare their federal income tax return. The data contained in the file named TaxReturn are consistent with the study results. These data provide the time in hours required of 40 individuals to complete their federal income tax return. Using past years' data, the population standard deviation can be assumed known with standard deviation = 9 hours.

What is the 95% confidence interval estimate of the mean time it takes an individual to complete a federal income tax return (to 1 decimal)?

__________ _______________ hours

Solution Summary

As data file is not attached, sample mean can not be calculated. However the Solution provides the method of calculating the Confidence Interval assuming the sample mean as x-bar.