Question

1. A random sample of n textbooks prices is taken from a local college bookstore. The mean of the sample is 74.22, and s = 25. If the margin error E is 6.9. Find the following:

1. For an 86% confidence level, determine the confidence interval around the population mean.
2. Find the sample size, n?.  

Answer 1

a) The 86% confidence interval for population mean is

xbar - E < < xbar + E

74.22 - 6.9 < < 74.22 + 6.9

67.22 < < 81.12

This is 86% confidence interval for population mean

b)

We have ^ = s = 25

E = 6.9

c = confidence level = 0.86

The required sample size n

n = ( Z​​​​​​a/2* ^)2/ E​​​​​2

For a = 0.14 , Z​​​​​​a/2 = Z​​​​​​0.07 = 1.48

n = ( 1.48*25)2/ 6.92

n = 29