National manufacturer of ball bearings is experimenting with two different processes for producing precision ball bearings. it is important that the diameters be as close as possible to an industry standard. the output from each process is sampled and the average error from the industry standard is calculated. the results are presented below. process a process b mean 0.002 mm 0.0026 mm standard deviation 0.0001 mm 0.00012 mm sample size 12 14 the researcher is interested in determining whether there is evidence that the two processes yield different average errors. assume that the population standard deviations are equal. this example is what type of test?