I'm a primary school teacher who was challenged by a year 5 child to explain how to solve the following without switching and negating.
1234 - 4321 =
I acknowledge that I would switch the numbers so as to solve 4321 - 1234 in a written column method and then make the answer negative, but was at a loss to explain why it couldn't be solved without doing this.
Surely, mathematically, it can be written in columns with 1234 above the 4321 and then solved as 1234 - 4321 by exchanging/borrowing?... or can it not?
Bye for now.