Can i mix 4GB of RAM with 8GB?



Can you? Maybe. Should you? Absolutely not!

Even if your motherboard/cpu supports hybrid mode, 4GB of your memory will be much slower to access. For systems that don't support hybrid, the entire thing will run in single channel mode and be really slow. 2x8GB isn't that expensive right now, might as well just get that and never worry about upgrading for the life of the cpu