Determine which case would you use to solve the following problem: A sample of 1

Question

Determine which case would you use to solve the following problem: A sample of 12 concrete cylinders were tested for compression. The sample mean of failure stress was 6,256 psi, and the sample standard deviation was 467 psi. At the 5% level of significance, can it be said that the population variance of the failure stress is at most 7,000 psi?

(a) Case 1 of Confidence Intervals

(b) Case 2 of Confidence Intervals

(c) Case 3 of Confidence Intervals

(d) Case 1 of Hypothesis Tests, Question 3

(e) Case 3 of Hypothesis Tests, Question 3

(f) Case 4 of Hypothesis Tests, Question 1

Explanation / Answer

Ho: o^2<=7000
Ha: o^2 > 7000
The test statistic is
Chisquare =(12-1)*(467)^2/7000
=11*15.444/10
= 342.711
Given a=0.05, the critical value of chisquare with, df=n-1=11 is 19.68 (from chisquare table)
Since 19.68 is less than 342.711, we reject Ho.
So we can conclude that the variance in the population failure stress is n't at most 7,000 psi  

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