I wrote a (very long) blog post about those viral math problems and am looking for feedback, especially from people who are not convinced that the problem is ambiguous.
It's about a 30min read so thank you in advance if you really take the time to read it, but I think it's worth it if you joined such discussions in the past, but I'm probably biased because I wrote it :)
The ÷ sign isn't used by "Americans", it's used by small children. As soon as you learn basic mathematical notation in your introductory algebra class, you've outgrown the use of that symbol.
Children here in the Netherlands use : as a divisor symbol. I don't know whether the ÷ sign is particularly American, but it's not universal.
I don't know where you're from, but it's used universally in Australia - textbooks, calculators, all ages - and from what I've seen the U.K. too.