Question 137843: I am having a lot of trouble with a couple of questions. Can someone please explain and help me with them?
1) What is the 90% confidence interval for the variance of exam scores for 28 algebra students, if the standard deviation of their last exam is 12.7?
A) 108.6
B) 10.4
C) 123.7
D) 122.8
2) A sample of 23 European countries found the variance on life expectancy was 7.3 years. What is the 95% confidence interval for the variance of life expectancy in Europe?
A) 27.2
B) 5.6
C) 4.4
D) 28.9
Thank you for your help.
Answer by stanbon(75887)   (Show Source):
You can put this solution on YOUR website! 1) What is the 90% confidence interval for the variance of exam scores for 28 algebra students, if the standard deviation of their last exam is 12.7?
A) 108.6 B) 10.4 C) 123.7 D) 122.8
(28-1)(12.7)^2/43.194 < sigma^2 < (28-1)(12.7)^2 /14.573
100.827... < sigma^2 < 298.83
Comment: The answers you are given are for the 90% confidence interval
lower limit for the standard deviation. If you take the square root of
the lower limit for sigma^2 you get 10.04 which is answer B.
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2) A sample of 23 European countries found the variance on life expectancy was 7.3 years. What is the 95% confidence interval for the variance of life expectancy in Europe?
A) 27.2 B) 5.6 C) 4.4 D) 28.9
(23-1)7.3/36.781 < sigma^2 < (23-1)7.3/10.982
4.3664 < sigma2 < 14.624
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I have no idea what your A,B,C,D answers might mean.
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The formula I am using is as follows:
[(n-1)s^2/(Ch-Sq Right)] < sigma^2 < [(n-1)s^2/Ch-Sq Left)]
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cheers,
Stan H.
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