In: Statistics and Probability
Find the 80% confidence interval for the standard deviation of the ages of seniors at Oak Park College if a random sample of 21 students has a standard deviation of 2.3 years. Assume the variable is normally distributed.
Solution :
Given that,
s = 2.3
s2 = 5.29
2R = 2/2,df = 28.412
2L = 21 - /2,df = 12.443
The 80% confidence interval for is,
(n - 1)s2 / 2/2 < < (n - 1)s2 / 21 - /2
(20)(5.29) / 28.412 < < (20)(5.29) / 12.443
1.93 < < 2.92
(1.93 ,2.92)