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This documentation will show you how to verify and change the aggregation method by which your grade book will be calculated if needed.
First, locate the Administration block (typically in the left sidebar region of the course page). Under Course administration click on Gradebook setup. (OR once in the grades, click the Setup tab. )
Once in the 
Select the Test you want to make the changes on.
Head over to Gradebook Setup.
Once in the Setup tab, click the Edit button the applies to the entire grade book (highlighted abovebelow).
Within the menu that pops up, click Edit settings. This will take you to the overall grade book settings for your course.
Under the Grade category section, you will see and drop down menu for Aggregation. Select you desired aggregation method from the drop down menu. NOTE: View descriptions of each aggregation method.
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When you have made all your changes, remember to click Save changes.
Back on the Setup tab, you will see that the aggregation method you selected will be shown below Course total.
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