Lets take the sample of books from the library by picking 2 books from each shelf and note the age of each of the book,

We took a sample of 64 books and found that the mean age is 52 years and the standard devaition is 6 years.

Now the (1 - o ) 100% confidence interval for the mean age of the books is given by za/2, + n Za/2 n Let the confidence level is 0.05, Then Za/2 = 1.96 Hence the confidence interval is 6 52 1.96), 52 + 6 Vna/2, 3+ Vn #0/2 (1.96) V64 V64 = (50.53, 53.47)