system
A chat on subreddit /r/me_irl
human
At least where I’m from in the US we don’t add an ‘s’ but that’s like the smallest change
gpt
Im a us citizen as well, but not bothered by "maths" because it is technically correct. Context "I'll have to check the mathematics" the s is indicative of plural, so the abbreviated form would be "I'll have to check the maths" 

Or I could just be pulling all that outta my ass. I'm bad at math and I probably fucked up the English trying to explain my reasoning.