Assume that each sample is a simple random sample obtained from a normally distributed population. Use Table 7-2 to find the indicated sample size.

Data in Table 7-2

You want to estimate σ for the population of diastolic blood pressures of air traffic controllers in the United States. Find the minimum sample size needed to be 95% confident that the sample standard deviation s is within 1% of σ. Is this sample size practical?

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To be 95% confident that s is within ... 1% 5% 10% 20% 30% 40% 50% To be 99% confident that s is within... 1% 5% 10% 20% 30% 40% 50% σ of the value of σ, the sample size n should be at least 19,205 768 192 48 21 12 8 of the value of σ, the sample size n should be at least 33,218 1,336 336 85 38 22 14