Historical data indicate that the standard deviation of a process is 6.7.

a. A recent sample of size 28 produced a variance of 66.5. Test to determine if the variance has increased using a significance level of 0.05.

b. A recent sample of size 7 produced a variance of 8.48. Test to determine if the variance has decreased using a significance level of 0.025.

c. A recent sample of size 15 produced a variance of 61.6. Test to determine if the variance has changed using a significance level of 0.10.