Question

Use the given confidence level and sample data to find a confidence interval for the population standard deviation sigma . Assume that a simple random sample has been selected from a population that has a normal distribution.

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95 ​% ​confidence; n = 91​, x overbar = $65,200​, s = ​$16,815

Answer 1

Chi-square critical value at 0.05 level with 90 df = L = 65.647 , U= 118.136

95% confidence interval for is

sqrt [ (n-1) S² / U ] < < sqrt [ (n-1) S² / L ]

sqrt [ 90 * 16815² / 118.136] < < sqrt [ 90 * 16815² / 65.647]

14677 < < 19688

95% CI is ( 14677 , 19688)