The number system was enlarged to include, not only positive numbers, but negative numbers as well. Whole numbers such as 1, 2, 3, 4, and so on, plus the negative numbers, -1, -2, -3, -4, and so on, are called integers.

For each of the integers that are to the right of 0, there are numbers that correspond with them that are to the left of 0. Such as 1 corresponds with -1, 2 with -2, 3 with -3, and so on. It is a lot easier to make a timeline full of number 1 to 10 on the right side of 0, and -1 to -10 on the right side of the 0. You will then be able to see more clearer of what numbers correspond with what numbers.