17 A random sample of 20 items is selected from a population

17. A random sample of 20 items is selected from a population. When computing a confidence interval for the population mean, what number of degrees of freedom should be used to determine the appropriate t-value?

21

25

20

19

Solution

Here degree of freedom for the t-test is

df=n-1=20-1=19

where n shows the number of observations.