The Natural aggregation method will report a sum of all grades in the grade book.
One way to control the weighting of items in the grade book is to make each item worth the correct maximum number of points to match the desired weights.
Another way is to use the Weights column in the Gradebook setup screen:
Click the checkbox near each weight you wish to change. Then enter the new weight into the blank.
All other Weights will automatically adjust so that the sum of all Weights equals 100.
Return to the Setup Gradebook main resource page for more information on other topics.