Some students achieve consistent results on their schoolwork. They can accurately predict what their marks will be before the teacher has returned the work. But sometimes, students' results may vary greatly depending upon the amount of interest in the subject, the time spent studying, or even the amount of sleep the night before the test. One grade that is significantly higher or lower than the rest affects the overall average. It's important to know how to calculate averages to get a more accurate assessment of the learning that's taken place.

Write down the 2 grades you wish to average. If the grades are not yet expressed as a percentage, this conversion must be done first. Write the score that was achieved expressed as a fraction of the total marks available. For example, if the test was marked out of 20 and the student mark is 12, it will be written as 12/20.

Divide 100 by the bottom number, the total marks available. Multiple the top number, the student's score, by this number. For example, 100 / 20 = 5; 12 x 5 = 60. This result is the grade expressed as a percentage. Repeat this process with the second grade, so both are expressed as percentages.

Add the 2 percentage grades together and divide by 2. For example, if the first percentage grade is 60 and the second is 90, added together they equal 150, divided by 2 is 75. This is the average of the 2 grades. To find the average of more than 2 grades, follow the same procedure but divide the total score by the number of tests being averaged.