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 psi and psi, respectively.
(a) Using a 90% confidence interval on the difference in mean breaking strength, comment on whether or not there is evidence to support the claim that manufacturer 2 produces yarn with higher mean breaking strength.
(b) Using a 98% confidence interval on the difference in mean breaking strength, comment on whether or not there is evidence to support the claim that manufacturer 2 produces yarn with higher mean breaking strength.
(c) Comment on why the results from parts (a) and (b) are different or the same. Which would you choose to make your decision and why?