In previous lessons, students determined whether groups of objects and representations had an even or odd number of objects by creating 2 equal groups or by pairing objects.

In this lesson, students explore patterns in the ways they can represent even and odd numbers as sums of two addends. In the first activity, they decompose even and odd numbers in different ways and notice that only the even numbers of objects can be decomposed into two equal addends. In the second activity, students practice decomposing numbers into two equal addends and verify that even numbers can be represented as a sum of two equal addends. Students will continue to use expressions with equal addends to represent arrays in upcoming lessons and will relate multiplication expressions to addition expressions with equal addends in grade 3.

Throughout the lesson, it is important to emphasize that even numbers can be represented as a sum of two equal addends. Avoid communicating a misconception that odd numbers cannot be represented as a sum of two equal addends. (For example, the equation shows that they can.) Students will learn that odd numbers cannot be represented as a sum of two equal whole numbers as they learn more about whole numbers and fractions in later grades.