Covariance
Covariance (Sxy) is a measure of how much two random variables change together. It is expressed as the arithmetic mean of the product of the variations of each variable against its average.
Example: Given the previous marks you calculate, firstly, the product of the marks of each student. Then, you add those results and divide them by the number of students. Lastly, you subtract from it the product of the previously calculated averages.
