I want to assemble a new PC to play battlefield 3 so I have decided to by an Amd A6-3650 processor and graphics card is Radeon HD 6670 1Gb DDR3(multi gpu) also 4 Gb DDR3 Ram.
The other components are all OK in selection just get confused in processor and graphics card with multi gpu

Here are the specs for BF3: Battlefield 3 system requirements - Battlefield 3 (http://bf3blog.com/battlefield-3-system-requirements/)

While you should be fine with your config, it will soon be outdated.
Worth OVERspeccing any system and build and fast as you can afford.