Math CentralQuandaries & Queries


If a population has standard deviation 20, what is the minimum sample size to be 95% confident that the error should be accurate to within 4?


If you can assume that the population is approximately normal then the formula for the confidence limits is

confidence limits

Since you want a confidence interval with an error of ±4 you have

sample size

You know that s = 20 and α = 0.5, hence you can solve for n.


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