consistency

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

$\sum_{i=1}^n{(X_i-\overline X)}{(Y_i-\overline Y)}$

 =113.7384. What is the sample covariance?

选项：

0.7583

0.7633

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：

$Cov{(X,Y)}=\sum_{i=1}^n{(X_i-\overline X)}{(Y_i-\overline Y)}/{(n-1)}$=113.7384/149=0.7633

所以选择B选项。