Question 1×16gb 2×8gb

[Jonesy82]

I have 1×16gb and want to add 2×8gb is this possible?

 

[Phaaze88]

If your motherboard has more than 2 slots, yes, but it's not a good idea.
Does your motherboard support Flex Mode?

 

[Jonesy82]

If your motherboard has more than 2 slots, yes, but it's not a good idea.
Does your motherboard support Flex Mode?

No idea it's a gt51ch it has 4 slots only 1 is being used

 

[Phaaze88]

ROG GT51CH | Tower PCs | ASUS USA

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www.asus.com

Ok, they claim it supports up to quad channel - no mention of Flex Mode at all, even in the online manual.

Either way, mixing ram isn't a good idea.
You can still buy the 2x 8GB, but I recommend leaving the 16GB stick out, because:
-Ram is only guaranteed to work as sold.
-Mixing ram is always a gamble. Sometimes it works, sometimes not.
-The symptoms of incompatible ram won't always show up right away.
-Even sticks purchased separately, of the same brand and specs, can still fail - this is simply the scenario with the highest compatibility rate.

If you still choose to leave the 16GB in there along with the new kit, you will need to test for compatibility.
Prime95 Blend Test, AIDA64(limited free trial, unfortunately), and Memtest86 are all ways of testing this. I recommend doing at least any 2 of these 3 to confirm stability.