Gradebook

If you're showing us the whole of the cats and items screen (meaning there isn't anything below this, like category totals) then I'd say your agg methods are disabled forcing you to weighted mean of grades. I'd definitely disabled aggregate including subcategories because that will screw you up. I'd also consider whether you want to adjust your weights, do you want a 100-point item to be worth as much as a 5-point item? Know this doesn't talk to the issue but for that I'd suggest you enlist the admin for this Moodle instance into this conversation because I've never seen a gradebook forced into this condition.