Compute the weighted average. For example, as a teacher you grade your students based on quizzes and tests (quizzes are worth 40 percent and tests are worth 60 percent of the students' final grade). To obtain each grade, or weighted average, you must use the following operation:
Assume the student has a quiz average of 100 and a test average of 85:
(0.40 * 100) + (0.60 * 85) = 91
Repeat this step for each student to obtain all weighted averages.
Write down a list of the weighted averages. For example, if you have a class with three students, final year grades might be:
93 - Student 1
87 - Student 2
90 - Student 3
Add all of these final grades together and divide the sum by the number of students to get the average weighted grade. For example:
(93 + 87 + 90)/3 = 90
Subtract the mean weighted average grade in the class from each individual's weighted average and take the absolute value of each of those results. For example:
93 - 90 = 3
87 - 90= -3
90 - 90 = 0
Absolute value:
absolute value of 3 = 3
absolute value of -3 = 3
absolute value of 0 = 0
Add the absolute values together and divide by the number of total students. For example:
(3 + 3 + 0)/ 3 = 2
Thus, the weighted average deviation is 90 -+2.