In: Statistics and Probability
The breaking strength of yarn supplied by two manufacturers is being investigated. We know from experience with the manufacturers’ processes that σ1 = 5 psi and σ2 = 4 psi. A random sample of 20 test specimens from each manufacturer results in x¯1 = 88 psi and x¯2 = 91 psi.
(a) Show all steps (including how to find cutoff value) and construct a two-sided 90% Confidence Interval for the true difference in means. Draw a conclusion on whether yarn 1 and yarn 2 are significantly different using only the confidence interval constructed.
(b) Show all steps (including how to find cutoff value) and construct a two-sided 95% Confidence Interval for the true difference in means. Draw a conclusion on whether yarn 1 and yarn 2 are significantly different using only the confidence interval constructed.
( a )
yarn 1 and yarn 2 are significantly different because 0 does not lies between -5.355 and -0.645
( b )
yarn 1 and yarn 2 are significantly different because 0 does not lies between -5.806 and -0.194