If the coefficient of correlation r = −.81,the standard deviations of x and y are 20 and 25,respectively,then cov(x,y)must be −405.0.

Standard Deviations

An assessment measure that determines the degree of deviation or scattering of data points around the average.

Correlation R

A statistical measure known as Pearson's correlation coefficient that quantifies the degree and direction of linear relationship between two variables.

Cov(x,y)

The covariance between two variables X and Y, measuring how changes in one variable are associated with changes in a second variable.