In previous lessons, students learned to look for ways to decompose a number in an expression to get to a ten when adding or subtracting numbers mentally in Number Talks. They have learned to use this method when adding or subtracting larger numbers which require composing or decomposing a ten.
In this lesson, students use the number line to represent these methods. These methods do not require students to explicitly compose or decompose a ten. The number line helps students see how others use what they know about the structure of whole numbers, properties of operations, and place value (MP7) to add and subtract within 100. The number choices in the expressions used in this lesson are designed to elicit methods based on looking for ways to make a ten or get to a ten. However, many students may prefer to use other strategies or representations, such as base-ten blocks or diagrams, to find the values. Look for ways to connect these students with peers who use different methods and can explain why they chose their method based on what they noticed about the numbers in the expressions.
- Action and Expression
- On a number line, represent place value methods for solving addition and subtraction equations that may involve composing or decomposing a ten.
- Sumemos y restemos usando una decena.
Teacher Reflection Questions
- Number Puzzles: Addition and Subtraction (1–4), Stage 4: Within 100 with Composing (Addressing)
- Number Line Scoot (2–3), Stage 1: Twos, Fives, and Tens (Addressing)
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