Teachers can use the number line to show students how to add and subtract numbers, such as two positive or two negative numbers, and a positive with a negative number. For example, for the addition of 4 + 5, students need to locate 4 on the number line and count off five tick marks to the right of 4 to arrive at 9 on the number line.
A number line contains 0, negative numbers to the left of 0 and positive numbers to the right of 0. To add numbers together, students need to move to the right, however, to subtract, the student moves to the left. For example, when subtracting 10 - 6, the student should locate 10 on the number line and moves six tick marks to the left of 10 to reach 4.