For illustration, if the average grade of the whole class is 80 (which can also be regarded as X), the total score of the first group is15× 4+15× 80 =1260, or (80+4) ×15 =/kloc-0. Indeed, the average score of the first group is 4 points higher than the average score of the class, which is actually 4× 15=60 points more.

Similarly, the total score of the second group is (80-2) ×13 =10/4, and the second group is 2× 13=26.

The calculation principle of other groups is similar.

In your calculation,15× 4+13× (-3)+14× (-2)+12×1= 60-39-28+/kloc-.

The average score of the fifth group is 5 points, which means that the average score is lower than the class average.