Aggregation determines how grades in a category are combined, such as:
An aggregation type can be set for any of your categories.
Step 1: From within your course in Moodle open your grade book by selecting Gradebook setup from the Administration block menu.
Step 2: Click the Edit drop down menu located to the right of the category in the Actions column and select Edit settings.
Step 3: Select the aggregation type from the Aggregation drop down menu.
Step 4: When you are finished, click the Save changes button at the bottom.