In order to calculate the course total, an correct aggregation option needs to be selected. To select/change the aggregation option you can follow these steps: Go to the course page.
Click "Grades" link from the Course Administration.
On the top of new page, there is a setup menu of which first item is "Grader report". Select "Setup" from "Categories and items" section of the dropdown menu.
A table will be opened. Click edit button.
Click "Edit settings" menu on the dropdown menu.
On the "Aggregation" column click on the dropdown menu and select option you need.