Lack of available storage on my Samsung Galaxy Tablet

My samsung galaxy tablet is low on storage and i have no idea where the storage is being used. When I go into setting and look up storage I get a reading for the various sources documents,apps,pictures, etc. When I add up the usage I get about 5G. The usaged defined on the tablet is 15G. Where is the other 10G being consumed. Cache has all been cleared so I know it is not that and that should have been in the 5G anyways. Is it the operating system?