Question

In a random sample of 21 ?people, the mean commute time to work was 31.5 minutes and the standard deviation was 7.2 minutes. Assume the population is normally distributed and use a? t-distribution to construct a 80?% confidence interval for the population mean ?. What is the margin of error of ???

Interpret the results.

Answer 1

Sample size = 21

Degree of freedom = n-1 = 21 - 1 = 20

Sample standard deviation =7.2 minutes.

t critical value is 1.325

t critical value by using TINV(0.20,20)

the margin of error of ?

=2.0818

We can estimate population mean to within 2.0818 minutes with 80% confidence.

Confidence interval formula is

=>(29.42,33.58)........................a 80?% confidence interval for the population mean ?

We are 80% confident that population mean is between 29.42 minutes to 33.58 minutes.