Maybe if she knew that the second 10 was actually the first 10's negative, alter-world twin and when they meet they cancel each other out in a epic battle to the death her answer would be different. :B

(technically if the teacher shifted her methods to numbers having positive or negative attributes. For example 10 + 10 is a healthy relationship in which they add to each other and are happy and when it's 10 - 10 it's a toxic relationship xD)

xD of course! I think that was the unintentional idea behind the story.

There was always a lot of trouble with the term 'take away' for - . To a child, when something is "taken away" its subtracted from them and added to the taker. A lot like your more technical reply. xD

We got there in the end.