Lesson objective: Understand that fluency with numbers helps us to solve equations more efficiently.

Students bring prior knowledge of understanding addition as putting together and adding to and subtraction as taking apart and taking from (Grade K, Unit 10 K; K.OA.A.1). This prior knowledge is extended to using number partners of five to solve problems more efficiently. A conceptual challenge students may encounter is thinking that the strategies they have been using are the only strategies that can be used to solve problems. Students are also challenged to understand that efficiency in solving is a goal for addition and subtraction.

The concept is developed through work with number bonds, which provide a visual representation of the part-part-whole relationship.

This work helps students deepen their understanding of number because they will look at the part-part-whole relationship to see that knowing parts of numbers helps solve problems more efficiently. This will help students understand that a number can be broken into parts in different ways.

Students engage in Mathematical Practice 8 (Look for and express regularity in repeated reasoning) as they begin to understand the part-part-whole relationship in addition and subtraction. Students will begin to understand the commutative property of addition as they make efficient use of the partners for the number five.

**Key vocabulary:**

- fluency
- number bond
- number partners

**Special materials needed:**