When P1 represents the sum of the scores before students P2 represents the sum of the scores after learning of everyone Total instead of multiples of the number of students with a full score.
When P1 represents the sum of the score before every class. P2 represents the results of the latter class of people. Total represents the product of the number of students with full marks.
When P1 instead of the sum of pre-test everybody P2 instead of the sum of the posttest scores of everybody Total instead. The multiplication of the number of students with a perfect score