The phrase "a fairly simple system" is correct and usable in written English.
You can use it when describing a system that is not complex and is easy to understand or operate.
Example: "The software we developed is a fairly simple system that allows users to manage their tasks efficiently."
Alternatives: "a relatively easy system" or "an uncomplicated system".
We had a fairly simple system.
Behavior modification for A.D.H.D. is based on a fairly simple system of rewards and consequences.
Also the NES system as a whole is a fairly simple system and also provides some interesting material to simulate.
Tesco, Britain's largest supermarket chain, was able to take the lead in online groceries by devising a fairly simple system: goods ordered over the internet are picked from the shelves of the nearest supermarket and delivered to homes within set time slots.
It's a fairly simple system.
What's interesting about this launch is that it introduces a fairly simple system for managing bad actors on the service — something that Twitter itself could learn a thing or two from, in fact.
Mountain lakes in national parks or a national forest are fairly simple systems without a lot of human impact, which makes them fairly straightforward to study and manage.
It was a fairly simple administrative system, built around the ducal household, which consisted of a group of officers including stewards, butlers, and marshalls.
The game uses a fairly simple combination system so that players can chain attacks together; the highest possible attack combo being 10.
Some charming youngsters from Cornell have created a fairly simple and effective face matching system using a webcam, a little LCD read-out, and a tiny Atmel ATmega644 8-bit microcontroller running a set of Eigenface tests on the face in question.
Ogawa says the new system is a fairly simple one, and he hopes other researchers will attempt to replicate it.
