- Integers are closed for addition and subtraction both. That is, a + b and a – b are again integers, where a and b are any integers. - Addition is commutative for integers, i.e., a + b = b + a ...

Ellis showed a subtraction problem, performed both using the traditional regrouping, or borrow-and-carry, algorithm and using an example from the common core. Here’s a screenshot of the two methods.