问题如下：
Alice wants to research the variables X and Y, and the relationship between them. First, she chooses 150 samples and gets some summary statistics about these two variables. One of them is "Sum of cross-products of deviations from the mean", which is
=113.7384. What is the sample covariance?
选项：
A. 0.7583
B. 0.7633
C. 0.7532
解释：
B is correct.
考点: Calculate and Interpret Correlation Coefficients.
解析: 变量X和Y的协方差计算如下：
=113.7384/149=0.7633
所以选择B选项。
老师一级讲义上协方差的公式没有要除以n或者n-1啊 这里解析里的公式为什么要除以