A librarian wants to estimate the average number of books that library patrons r

Question

A librarian wants to estimate the average number of books that library patrons read per year. He would like to be 90% confident that his estimate is accurate to within + or - 4 books.

a. What additional information does the librarian need to choose a sample size?

A. The sample standard deviation
B. The approximate population proportion, or 0.5
C. The sample mean
D. The population mean

b. Preliminary results suggest that the value the librarian needs from part a is about 16.6. Find the minimum sample size that the librarian should use.

Explanation / Answer

(a) N = (z * s/E)^2, so sample standard devaition is required. Option (A)

(b) z- score for 90% confidence is z = 1.6449

N = (z * s/E)^2 = (1.6449 * 16.6/4)^2 = 47

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