What are "weighted grades"?
Weighted Totals in the Blackboard Grade Center
Weighted totals are calculated based on percentages; they are not based on grading schemas/letter grades. Columns included in the Weighted Total are not displayed using the same grading schema as the input grade values. Grading schemas simply map a range of percentages to a particular label for display purposes (i.e. 90%-100% = A). They do not have an impact on the weighted total's underlying calculations, which are based on percentages or points/points possible
Also see the question: