Question

An operation is commutative if you can change the order of the numbers involved without changing the result. Addition and multiplication are both commutative. Subtraction is not commutative: 2 - 1 is not equal to 1 - 2. So my question is what’s the difference between 2 - 1 and 1 - 2?

Answer 1

2-1=1 and 1-2=-1

Answer 2

2-1 = 1 and 1-2 = -1.
So the difference is 2.

If you asking why it is that way, it just IS. It can be deduced logically from how subtraction is defined.

Answer 3

There is no difference between 1-2 and 2-1 if you disregard the + or - in the final answer.

Sometimes when I do calculations on the calculator and I forget which number is the larger, I will end up with a negative answer. I just remember that the answer should be positive. Look at the equation and you can see if the answer should be + or -.