Examining a set of scores using a variety of methods gives you different results. The average or mean score, along with the mode and median, all show a tendency of the scores, but these three numbers will likely be different for the same information. Of these three, the mean score will be preferred, especially if most of the scores have similar values.
Add up all of the scores together. For example, add together scores of 100, 90, 100, 85, 95 and 80 to total 550.
Count the number of scores you have. For example, the data set of 100, 90, 100, 85, 95 and 80 has six pieces of data.
Divide the total of the scores by the number of scores to calculate the average score. For the example: 550/6 = 91.667.