Question

The data to the right represent the age​ (in weeks) at which babies first crawl based on a survey of 12 mothers. It is known that the data are normally distributed and that

s=13.23

weeks. Construct a

29	59	35	35
51	20	32	54
26	54	44	25

90​% confidence interval for the population standard deviation of the age​ (in weeks) at which babies first crawl.

The 90​% confidence interval is (____​ , ____​).

​(Use ascending order. Round to two decimal places as​ needed.)

Answer 1

Chi square critical values at 11 df with 0.10 significance level = 4.575 , 19.675

90% confidence interval for is

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

Sqrt [ 11 * 13.23² / 19.675 ] < < Sqrt [ 11 * 13.23² / 4.575 ]

9.89 < < 20.51

90% CI is ( 9.89 , 20.51 )