A Professor Grades 120 Research Papers and Reports That the Average

Multiple Choice

A professor grades 120 research papers and reports that the average score was an 80%.What do we know about the sum of the differences of these 120 scores from their mean of 80%?

A) The sum of the differences is minimal.
B) The sum of the differences is 80%,the same as the mean.
C) The sum of the differences is equal to zero.
D) It is impossible to know without knowing each of the 120 scores.