9.2
c)2.060
d)1.721

9.11
(128.17,147.03)

9.22
a)cannot tell, mean unknown
b)In the long run, 95% of the intervals obtained using this procedure will cover.

9.23
a) t=3.089>2.681=t(.01,df=12) thus Reject H0
b)26.62+/-1.782*4.56/sqrt(13)=(23.38,29.86)

9.35
a)(1.28,12.28)
b)t=-3.53, Reject H0
c)15 doesn't fall within the 95% confidence interval. so reject H0.