A random sample of 20 observations is selected from a normally distributed population. The sample variance is 12. What is the upper limit of the 95% confidence interval for the population variance?
A) 6.940
B) 7.564
C) 22.536
D) 25.599

Question

Quizplus · Accepted Answer

The upper limit of the 95% confidence interval for the population variance can be calculated as:
(n-1)*sample variance / Chi-Square value
Here, n = 20 (sample size), sample variance = 12, and for 95% confidence interval with 19 degrees of freedom (n-1), the Chi-Square value is 32.852 (from Chi-Square table or calculator).
Therefore, the upper limit is:
(20-1)*12 / 32.852 = 8.402
Rounding off to three decimal places gives the answer as 8.402, which is closest to option D (25.599).

A Random Sample of 20 Observations Is Selected from a Normally