Maria is a college professor, and she wonders how the scores compare on her midterm and her final. She teaches two sections of a course, and each section has 180 students. She decides to take a random sample of 10
students from each section. For those students, she'll calculate the mean midterm score and the mean final
score. She plans to look at the difference (Final - Midterm) between those means.
Consider the formula:
02 02
021-22 =
+
V ni
722
Why is it not appropriate to use this formula for the standard deviation of Tp - EM?