Question

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The weights of 22 randomly selected mattresses were found to have a standard deviation of 3.17. Construct the 95% confidence interval for the population standard deviation of the weights of all mattresses in this factory. Round your answers to two decimal places.

Answer 1

df = n - 1 = 22 - 1 = 21

Chi square critical values at 0.05 level with 21 df = 10.283 , 35.479

95% confidence interval for is

Sqrt [ (n-1) S² / /2] < < Sqrt [ (n-1) S² / 1-/2]

Sqrt [ (22 -1) * 3.17² / 35.479 ] < < Sqrt [ (22 -1) * 3.17² / 10.283]

2.44 < < 4.53

95% CI is ( 2.44 , 4.53 )