I have 4x4gb sticks of ram for 16 gb in all. One of the sticks is not functional anymore. When looking online to replace it, there is a 2x4gb pack and i can just keep the spare, but theres a 1x8gb stick of the same ram i use which is cheaper. can i use that 8gb stick along with the other 3 4gb sticks already in my pc? That would make 20gb of ram instead of 16. or does it need to be a 4gb stick like the others? thank you