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The percentage of titanium in an alloy used in aerospace castings is measured in 51 randomly selected parts. The sample standard deviation is s = 0.37 and the probability plot support the assumption that the population is normally distributed. Construct a 95% two-sided confidence interval for ?.

Answer :

A 95% two-sided confidence interval is 0.46 < a <0.31 .

The formula for confidence interval for population standard deviation is,

[tex]s\sqrt{\frac{n-1}{X^{2} _{1-a/2,n-1} } }[/tex]  < a < [tex]s\sqrt{\frac{n-1}{X^{2} _{a/2,n-1} } }[/tex]

Given in question,

Significance level, a = 1 - 0.95

                                 = 0.05

Sample size, n = 51

Sample standard deviation, s = 0.37

By using chi-square distribution table, we get

[tex]X^{2} _{1-a/2,n-1}[/tex] = [tex]X^{2} _{0.975,50}[/tex]

                  = 32.36

[tex]X^{2} _{a/2,n-1}[/tex] = [tex]X^{2} _{0.025,50}[/tex]

              = 71.42

Confidence interval for population standard deviation is :

[tex]0.37\sqrt{\frac{50}{32.36} }[/tex]  < a  < [tex]0.37\sqrt{\frac{50}{71.42} }[/tex]

0.45992018426 < a < 0.30958278534

Hence, a 95% two-sided confidence interval is 0.46 < a <0.31 .

To learn more about confidence interval here:

https://brainly.com/question/24131141

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