Unit Plan 22 (Grade 2 Math): Number Lines—Adding & Subtracting Lengths
Use open number lines to model addition and subtraction within 100, showing jumps for length problems; choose helpful scales, explain strategies, and check answers for reasonableness.
Focus: Deepen number-line representations for sums and differences; use jumps and open number lines to solve length problems in context.
Grade Level: 2
Subject Area: Mathematics (Measurement & Data • Operations • Math Practices)
Total Unit Duration: 5 sessions (one week), 35–45 minutes per session
I. Introduction
Students extend number-line thinking by building accurate number lines, choosing a useful unit length (1s, 5s, or 10s), and showing addition as jumps to the right and subtraction as jumps to the left. They use open number lines to flexibly represent strategies (count on, make a ten, break into tens/ones) for real-world length problems (MP.5).
Essential Questions
- How do I choose a helpful unit length and scale on a number line?
- How do jumps show addition and subtraction in length stories?
- How can an open number line help me explain and check my strategy?
II. Objectives and Standards
Learning Objectives — Students will be able to:
- Construct and label number lines with consistent tick marks and a chosen unit length.
- Represent addition and subtraction within 100 as jumps on a number line (right for add, left for subtract).
- Solve one- and two-step length word problems and match models to equations.
- Select tools (rulers, strips, open number lines) and explain strategy choices (make a ten, tens then ones).
- Check reasonableness by estimating and/or using a second method.
Standards Alignment — CCSS Grade 2
- 2.MD.6: Represent whole-number sums and differences within 100 on a number line diagram with equally spaced intervals; represent whole numbers as lengths and sums/differences of lengths.
- 2.OA.1: Use the four operations to solve word problems within 100, including two-step problems, using drawings and equations with a symbol for the unknown.
- Mathematical Practice — MP.5: Use appropriate tools strategically (rulers, open number lines, manipulatives) to model and solve.
Success Criteria — Student Language
- I can draw and label a number line with equal ticks and a clear unit length.
- I can show addition as jumps to the right and subtraction as jumps to the left and write an equation that matches.
- I can explain why I chose my jumps/scale, and I can check my answer another way.