Arithmetic

Hold on, that’s the same in all languages… isn’t it?

Well, not always. Conventions change: the advent of computing brought the asterisk for multiplication and the slash for division, for instance, neither of which were around when I was a kid, and the mid-height decimal point dropped onto the line. And there are different conventions in different languages too.

• English doesn’t use a colon to denote division. Ratios and map scales are OK, but not the basic division operation. Use a slash if you have to or the obelus (division sign) ÷ if possible
• using “+/+” to indicate that a series of numbers or a table column should be summed or “-/-” to show that they should all be subtracted from the first one (I think… never quite got the hang of that one myself) aren’t an English notation
• using “+/-” or the plus-minus sign ± to mean “approximately” is a Dutch trick. English puts it between two numbers, defining a range. So 13±2 means anything from 11 to 15 (or sometimes more mathematically 13 with a standard deviation of two), and ±13 doesn’t really mean anything.

But yes, the actual arithmetic itself is the same for everyone. Fortunately!

Prevalence: low. Tables in financial reports can be a good source of confusion.
Frequency: medium. The colon not being used for division in English is one you need to be aware of.
Native: no. As I said in the preamble, conventions do change over time. But these specific ones are not English.