# The Rule of Change of Addends

The rule of change of the addends is a manifestation of the associativity of addition:

When one of the addends changes by a certain amount, the sum changes by the same amount.

The applet below illustrates that rule. In this applet, you may click on either of the two addends. Clicking a little to the right of the number's vertical central line will increase it by one. Clicking a little to the left of the central line decreases the number by 1. You start with the common fact

What if applet does not run? |

## Related material
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