A set of batteries is used in a research satellite. The satellite can only run on one battery, but runs best if more than one is used. Engineers have determined that a variance of 2 = 18 months is most desired. A random sample of 30 batteries gave a sample variance of s2 = 17.2 months
Find a 95% confidence interval for the population variance of the batteries
This is all the info I have. Can anyone help me figure out where to start?
2007-12-01 11:13:43 · 3 answers · asked by Anonymous in Science & Mathematics ➔ Mathematics
The confidence interval for the variance is:
(n - 1)s² / XR² < σ² < (n - 1)s² / XL²
where XR² and XL² are chi square values with n - 1 degrees of freedom and
P( X² > XR² ) = (1 - α) / 2
P( X² < XL² ) = (1 - α) / 2
in this case:
α = 0.95
XL² = 16.79077
XR² = 46.97924
the CI is thus:
10.61746 < σ² < 29.7068
this is extremely sensitive to the assumption of normality.
2007-12-04 16:45:18 · answer #1 · answered by Merlyn 7 · 0⤊ 0⤋
Aww no we're getting taught this on Wednesday :(
If it was a confidence interval for anything else, I'd know.
For a start it's a random sample and n is 30, so central limit theorem says it's normally distributed, means you use critical values from the normal distribution rather than the t-distribution.
I'm really not sure :(
2007-12-01 11:20:08 · answer #2 · answered by Rick G 4 · 0⤊ 2⤋
I am 95% confident that somebody else will help you figure out what to start.
2007-12-01 11:17:23 · answer #3 · answered by Anonymous · 0⤊ 2⤋