>That’s wildly inaccurate. Arithmetic was very much a subject at several schools...

I'm talking specifically about "long division" in Europe... and have heard this factoid from multiple mathematicians including Nasim Taleb. So I expect there is a basis for the claim...

Well, especially Taleb's claims are worth it to source check. Especially if they are these really juicy stories (like only 5 people in Europe knowing long division).

He has bit of a habit exaggerating and elaborating on stories for the sake of making tasty reading. There was a story in Black Swan about two hospitals and a simple statistical riddle that he claimed professional statisticians would get wrong. It wasn't even a trick question, most people would get it right. I found this hard to believe but I was still sort of surprised when the source spoke of a much harder statistics question that was surveyed at a psychologists convention, not statisticians. That was the first (and the last) source I checked on him. I'd have checked a few more but I don't have the book any more.

But now I guess I can add this one to the list of examples.

Let’s be clear, if you mean the modern notation, that was was ‘invented’ after the dark ages. So under that definition it’s ~0 people world wide in the dark ages. Excluding independent discovery.

However, if we are talking about the number of people being able to accurately do 1234 / 56 = 22 r 2. That was regularly taught in the Middle Ages with plenty of examples of such calculations being available.