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.

Table 7-2

You want to estimate σ for the population of pulse rates for the population of marathon runners. Find the minimum sample size needed to be 99% confident that the sample standard deviation s is within 50% of σ. Is this sample size practical?

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% of the value of , the sample size n should be at least 19,205 768 192 48 21 12 8 of the value of , the sample size n should be at least 33,218 1,336 336 85 38 22 14