SOLUTION: What is the 90% confidence interval for the variance of exam scores for 28 algebra students, if the standard deviation of their last exam was 12.7?

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Question 1040405: What is the 90% confidence interval for the variance of exam scores for 28 algebra students, if the standard deviation of their last exam was 12.7?
Answer by robertb(5830) About Me  (Show Source):
You can put this solution on YOUR website!
[%28%28n-1%29s%5E2%29%2FX%5E2%5Balpha%2F2%5D,%28%28n-1%29s%5E2%29%2FX%5E2%5B1-alpha%2F2%5D ]
=[%2827%2A12.7%5E2%29%2FX%5E2%5B0.05%5D,%2827%2A12.7%5E2%29%2FX%5E2%5B0.95%5D ]
=[4354.83%2F40.113,4354.83%2F16.151 ]
= [108.564, 269.632]
where X%5E2%5Balpha%2F2%5D+ is the chi-square distribution with df 28-1 = 27, and alpha+=+0.10.