Can you use 2 x 2gb and 2 x 4gb of ram in an iMac 27inch mid 2011?

Hi everybody, Hope you're enjoying the summer holidays 🙂 Now, I've got an iMac 27inch 2011 model with the standard 4gb inside it (2 x 2gb) and I was wondering if I could add another 8gb (2 x 4gb)? Also would I see a major improvements in multitasking with 12 gb of ram?

Thanks 😀