Think of adding two integers as starting on the number line at the mark corresponding to the first integer and then moving from there by the amount of the second integer — going to the right if the second integer is positive and to the left if the second integer is negative.
The usual procedures for adding integers are simple and can be stated with two rules.
- To add two integers that are either both positive or both negative, add the two numbers (ignoring their signs) and then place the sign that the original numbers had on that answer.
- To add two integers that do not have the same sign (one is positive and one is negative), take the number that's bigger (ignoring the signs) and subtract the number that's smaller (still ignoring the signs). Then maintain the sign of the number farthest from zero on the number line.