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A Google search on "weighted grades" or "weighting grades" will yield hundreds of results. There are actually several ways you could word this, such as "final grade weight=200%" or "weighting of final grade is 2"
Having said all this, it seems strange that the final grade itself would have a weight, since it is the "final" grade. Normally, one or more components of the final grade would have weights which would give the final grade. That is, the parts of the final grade would be weighted, not the final grade itself.