A polymer mixing process must be run until the blending is
complete. A random sample of nine runs measuring the time to
complete blending, were recorded as (in hours):
14.82, 13.16, 12.86, 12.4, 12.98, 12.88, 13.86, 13, 13.1.
Assuming blending times are normally distributed but sample
size is too SMALL to assume s ≈ σ, construct a 90%
confidence interval for the true mean blending time.
tvalues for tail area α  

ν  0.100  0.050  0.025  0.010  0.005 
1  3.078  6.314  12.706  31.821  63.657 
2  1.886  2.920  4.303  6.965  9.925 
3  1.638  2.353  3.182  4.541  5.841 
4  1.533  2.132  2.776  3.747  4.604 
5  1.476  2.015  2.571  3.365  4.032 
6  1.440  1.943  2.447  3.143  3.707 
7  1.415  1.895  2.365  2.998  3.499 
8  1.397  1.860  2.306  2.896  3.355 
9  1.383  1.833  2.262  2.821  3.250 
10  1.372  1.812  2.228  2.764  3.169 
Your answers can be rounded to three decimal digit accuracy when
entered.
Lower limit is =?

Level of Significance , α = 0.1
sample std dev , s = √(Σ(X x̅ )²/(n1) )
= 0.708
Sample Size , n = 9
Sample Mean, x̅ = ΣX/n = 13.2289
degree of freedom= DF=n1= 8
α/2 = 0.05
't value=' tα/2= 1.860 [from given
table]
Standard Error , SE = s/√n =
0.2360
margin of error , E=t*SE =
0.439
confidence interval is
Interval Lower Limit= x̅  E =
12.790
Interval Upper Limit= x̅ + E = 13.668
confidence interval is ( 12.7900 < µ
< 13.6678 )
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