not recommended to buy an additional stick and put it in.
since they didn't come in a kit together it's not guaranteed they will work well together.
stuff to do with timings and B-Dies etc. that I won't bore you with.
Also, I am recommending these sticks to you based on the assumption you live in America.
If you live in any other country please let me know as this will affect price and availability of components.
So just getting a new kit is recommended.
Here's a decent kit that's good for both Intel and Ryzen.
Memory:GeIL - EVO FORZA 16 GB (2 x 8 GB) DDR4-2400 Memory ($70.98 @ Newegg) Total: $70.98 Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2019-04-18 21:21 EDT-0400