10 You want to estimate for the population of waiting times

10.) You want to estimate for the population of waiting times at a fast-food restaurant’s drive-up windows, and you want to be 95% confident that the sample standard deviation is within 20% of . Find the minimum sample size needed. Is this sample size practical?

Solution

Margin of error = 0.2s

n = Z0.025 × s/ ME

= 1.96 × s/ 0.2s

= 1.96/0.2 = 9.8

n = 96.04 ~ 96

Yes the sample size is practical.