Two "add" two equals four

Hey guys, I was on DuoLingo recently and was marked down for translating something into English as “Two add two equals four”.
When I questioned this further on the forums there, someone told me that it is completely incorrect to use “add” in this way. This pretty much made me question my very existence.
I’m a native English speaker from the UK and I’m sure I’ve heard “add” used this way enough for it to be part of the common tongue. I’d even say I was taught with the phraseology in school by numerous different teachers.
I just wanted to check that I’m not going crazy and that it’s correct to use “add” this way. I’m well aware that you can use “plus” or even “and” in phrases like this too, but is this just a British way of using “add” or something like that?

IMO non-standard but something you might hear once in a while.

It’s strictly a mathematically term, two PLUS two EQUALS four.

Anything else is incorrect, or British.,

Speaking as a native British speaker (from Scotland), that doesn’t sound natural to me. It may well be correct in the native dialect of some of your teachers, but if Duolingo is going for either Standard American or British English, I think they’re right to reject it as unidiomatic.

I too am from Scotland xD

I consider myself fairly well spoken and it sounds fine to me, which is why I was so confused when someone tried to correct it. Just as I’ve heard the opposite used, aka: “Two take away two equals zero”