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A sample of 12 joint specimens of a particular type gave a sample mean proportional limit stress of 8.55 MPa and a sample standard deviation of 0.76 MPa. (a) Calculate and interpret a 95% lower confidence bound for the true average proportional limit stress of all such joints. (Round your answer to two decimal places.) MPa

Sagot :

Answer:

95% of the lower confidence interval for the true average proportional limit stress of all such joints

7.7829

95% of the confidence interval for the true average proportional limit stress of all such joints

(7.7829, 9.3171)

Step-by-step explanation:

Step(i):-

Given that the sample size 'n' = 12

Mean of the sample = 8.55

The standard deviation of the sample (S) = 0.76

Step(ii):-

95% of the confidence interval is determined by

[tex](x^{-} - t_{\frac{\alpha }{2} } \frac{S}{\sqrt{n} } , x^{-} + t_{\frac{\alpha }{2} } \frac{S}{\sqrt{n} })[/tex]

Degrees of freedom = n-1 = 12-1 = 11

t₀.₀₂₅ = 3.4966

[tex](8.55 - 3.4966\frac{0.76}{\sqrt{12} } , 8.55 + 3.4966 \frac{0.76}{\sqrt{12} })[/tex]

(8.55 - 0.7671 , 8.55+0.7671)

(7.7829, 9.3171)

Final answer:-

95% of the confidence interval for the true average proportional limit stress of all such joints

(7.7829, 9.3171)