Lesson objective: Find three addends that equal the given sum.

This lesson helps to build fluency with addition of three addends. Connecting cubes are used here because they support decomposing and composing numbers. A number line is also used to help support this concept. This work develops students' understanding that we can add more than two numbers.

Students engage in Mathematical Practice 2 (Reason abstractly and quantitatively) as they determine combinations of three addends that make a given sum using objects or drawings. Students will also engage in Mathematical Practice 7 (Look for and make use of structure) as they manipulate and decompse the target number to determine the three missing addends, students may use the stucture of our number system such as base ten to help with decomposing.

**Key vocabulary:**

**addend: **one of the numbers in an indicated sum of two or more numbers (e.g., 4 + 3 + 1 = 8; 4, 3, and 1 are addends)
**decompose: **to break a number into smaller units to simplify computation
**digit: **any one of these ten numerical symbols: 0, 1, 2, 3, 4, 5, 6, 7, 8, or 9
**equal: **having the same amount, size, number, or value
**number line: **a line on which a point represents a value or number
**sum: **the result when two or more quantities are added

**Special materials needed:**

- digit cards
- game directions
- linking cubes
- number lines (0-20)
- record sheets
- sum cards