HOW to mix these RAMs?

Solution
What mobo and CPU? In general I'd try (on a dual channel mobo) the 8GB stick by itself in slot 1 closest to the CPU, manually set to 160 11-11-11-30 and DRAM voltage to 1.575, save, exit shutdown then install the 4GB sticks in slots 3-4 from CPU (if a relatively recent mobo all will run in dual channel) and give it a try. If no joy let us know mobo and CPU and we can try adjustments
I recommend a good blender and a sprig of mint.

Well, they aren't a great match.

Corsair is DDR3 1600 9-9-9-24 @ 1.5 volts
Adata is DDR3 1600 11-?-?-? @ 1.5 volts

You could install one at a time and then look at the JEDEC timings in the BIOS or using CPU-Z.

But basically you'll need to set the timings to the higher numbers to hopefully have that working.
 
Art sculpture perhaps

Can't be specific without knowing what kind of system they are going in, but most consumer systems in recent years use dual channel RAM which means you really want to install RAM in pairs.

You also want to have them all the same size, same timings, same voltage. Can you get them to work ? Possibly. Would I put in the effort ? No. I'd spend $20 more for a 2 x 8GB set

Best you can do is stick them all in according to the pic in your MoBo manual, set speed, timings and voltage to the lowest common denominator. If it don't work, reduce timings and or raise voltage and keep trying.
 
They have the same voltage, same speed, etc. The only thing not the same is the latency where the ADATA is 11, Corsair is 9, BUT, on corsairs sight it says that the vengeance can get up to an 11 latency.
 


11 is worse than 9, so you need to change the corsair to 11. It might or might not work, if it does you might generate bsods and memory errors every now and then, if it doesn't there's not much to be done.
 
What mobo and CPU? In general I'd try (on a dual channel mobo) the 8GB stick by itself in slot 1 closest to the CPU, manually set to 160 11-11-11-30 and DRAM voltage to 1.575, save, exit shutdown then install the 4GB sticks in slots 3-4 from CPU (if a relatively recent mobo all will run in dual channel) and give it a try. If no joy let us know mobo and CPU and we can try adjustments
 
Solution