1 You want to estimate for the population of waiting times a

1.) 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 = (z*(s.d) /ME) ²

n = (1.96 × s/ 0.2s)²

= (1.96/0.2)²

= 96.04

The required sample size is 97 ( rounded up)

Yes, the sample size is practical.