Kody wants to test to be sure his soap dispenser design works fairly for people with different skin colors. He selects separate random samples of 25 workers with light skin and 25 with dark skin. For each worker, he
measures the maximum distance from the dispenser at which it detects the employee's hand. Then he looks at
the difference in the sample means ( Light - TDark).
What do we know about the shape of the sampling distribution of Light - TDark, and why?