AARP reported on a study conducted to learn how long it takes individuals to pre
ID: 2624225 • Letter: A
Question
AARP reported on a study conducted to learn how long it takes individuals to prepare their federal income tax return (AARP Bulletin, April 2008). The data contained in the file named TaxReturn are consistent with the study results. These data provide the time in hours required for 40 individuals to complete their federal income tax returns. Using past years' data, the population standard deviation can be assumed known with ? = 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)?
Explanation / Answer
It requires the sample mean
Confidence interval for population mean (Mu) is
sample mean +/- confidence coefficient *standard error of mean
Sample mean ????
Confidence coefficient is the critical value of z for 95% confidence level = 1.96
Standard error of mean = sigma/sqrt n
= 9/sqrt 40
= 1.42
Substitute the values in the above formula after calculating the sample mean for constructing the confidence interval.