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### Unit 6: Lesson 1

Properties of numbers

Explore the commutative, associative, and identity properties of addition.
In this article, we'll learn the three main properties of addition. Here's a quick summary of these properties:
Commutative property of addition: Changing the order of addends does not change the sum. For example, 4, plus, 2, equals, 2, plus, 4.
Associative property of addition: Changing the grouping of addends does not change the sum. For example, left parenthesis, 2, plus, 3, right parenthesis, plus, 4, equals, 2, plus, left parenthesis, 3, plus, 4, right parenthesis.
Identity property of addition: The sum of 0 and any number is that number. For example, 0, plus, 4, equals, 4.

The commutative property of addition says that changing the order of addends does not change the sum. Here's an example:
4, plus, 2, equals, 2, plus, 4
Notice how both sums are 6 even though the ordering is reversed.
Here's another example with more addends:
1, plus, 2, plus, 3, plus, 4, equals, 4, plus, 3, plus, 2, plus, 1
Which of these is an example of the commutative property of addition?

The associative property of addition says that changing the grouping of the addends does not change the sum. Here's an example:
start color #11accd, left parenthesis, 2, plus, 3, right parenthesis, plus, 4, end color #11accd, equals, start color #e07d10, 2, plus, left parenthesis, 3, plus, 4, right parenthesis, end color #e07d10
Remember that parentheses tell us to do something first. So here's how we evaluate the left-hand side:
empty space, start color #11accd, left parenthesis, 2, plus, 3, right parenthesis, plus, 4, end color #11accd
equals, 5, plus, 4
equals, 9
And here's how we evaluate the right-hand side:
empty space, start color #e07d10, 2, plus, left parenthesis, 3, plus, 4, right parenthesis, end color #e07d10
equals, 2, plus, 7
equals, 9
Notice that both sides sum to 9 even though we added the 2 and the 3 first on the left-hand side, and we added the 3 and the 4 first on the right-hand side.
Which of these is an example of the associative property of addition?