Question

A chocolate chip cookie manufacturing company recorded the number of chocolate chips in a sample of 60 cookies. The mean is 23.05 and the standard deviation is 2.75. Construct a 80​% confidence interval estimate of the standard deviation of the numbers of chocolate chips in all such cookies.

Answer 1

Chi square critical values at 0.20 level with 59 df = 45.577 , 73.279

80% confidence interval for is

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

Sqrt [ 59 * 2.75² / 73.279 ] < < Sqrt [ 59 * 2.75² / 45.577 ]

2.4675 < < 3.1289

80% CI is ( 2.4675 , 3.1289 )