A 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. 
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. What is the degrees of freedom?
Definitions:
Normal Distribution
A bell-shaped data distribution where most observations cluster around the central peak and the probabilities for values further away from the mean taper off equally in both directions.
Sample Proportion
The fraction or percentage of a sample that exhibits a particular trait or attribute.
Population Proportion
The percentage of individuals in a population who share a certain characteristic or attribute.
Expected Value
The expected value of a random variable is the long-run average value of repetitions of the experiment it represents.
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