This graphic illustrates the equation a + b on a number line. Use the sliders a and b to adjust the values. For example, if you set slider a = 2 and slider b = 3, the number lines should show 2 + 3 = 5.
Try the following:
1. What happens when a and b are both positive? Is their sum positive or negative?
2. What happens when a and b are both negative? Is their sum positive or negative?
3. Make a = 5. What happens to the sum when b = -1, -2, -3, or -4?
4. Make a = 5. What happens to the sum when b = -6, -7, -8, or -9?
5. Make b = 5. What happens to the sum when a = -1, -2, -3, or -4?
6. Make b = 5. What happens to the sum when a = -6, -7, -8, or -9?
7. How can you tell what the sign should be on the sum of a positive and negative number?