We are evaluating the sheet metal scrap rate in a contractor proposal. Based on a sample of 28 parts you calculate a mean rate of 6.50% (treat as 6.50) and a standard deviation of 1.20. Calculate a 80% confidence interval to be used to support negotiations.
Possible Answers:
6.08 ≤ μ ≤ 6.92
6.18 ≤ μ ≤ 6.82
6.20 ≤ μ ≤ 6.80
6.43 ≤ μ ≤ 6.57