Q4 p333
Q: A 95% confidence interval for a population mean was reported to be 152 to 160. If σ = 15, what sample size was used in this study?
A: The mean must be right in the middle of the CI, so here the mean, xbar, is 156. Therefore the Margin of Error was 4. Recall how we find the MofE in the first place? It is MofE =1.96*sigma/root n.
So in this case 4=(1.96 *15)/root n.
Switch the terms around so that root n = (1.96*15)/4 = 7.35 That’s the square root of the sample size, so square it to get n =54.02. ROUND UP to get n = 55
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