Unit Plan 13 (Grade 3 Math): Two-Step Word Problems & Reasonableness
Solve two-step word problems with unknowns in any position using equations and visual models, then use rounding and estimation to check for reasonableness and clearly justify solution steps.
Focus: Write and solve two-step problems with unknowns in all positions; use estimation/rounding to check for reasonableness.
Grade Level: 3
Subject Area: Mathematics (Operations & Algebraic Thinking • Number & Operations in Base Ten)
Total Unit Duration: 5 sessions (one week), 45–60 minutes per session
I. Introduction
Students practice solving two-step word problems involving all four operations and writing equations with a letter for the unknown. They learn to estimate using rounding to the nearest 10 or 100 to check the reasonableness of answers. Emphasis is on choosing operations that match the context, showing work with bar models/tape diagrams, and explaining thinking.
Essential Questions
- How do I decide which operations (and in what order) a two-step problem needs?
- Why is it important to estimate and round to check my answer?
- How do equations and models help me explain my solution?
II. Objectives and Standards
Learning Objectives — Students will be able to:
- Read, plan, and solve two-step problems with unknowns in any position, using and explaining appropriate operations.
- Represent situations with equations that include a letter for the unknown and with bar models/number lines.
- Use rounding (nearest 10 or 100) and estimation strategies to judge reasonableness of results.
- Explain and defend solutions, including why a chosen operation order makes sense for the context.
Standards Alignment — CCSS Grade 3
- 3.OA.8: Solve two-step word problems using the four operations; represent with equations containing a letter for the unknown; assess reasonableness using mental computation and estimation strategies including rounding.
- 3.NBT.1: Use place value understanding to round whole numbers to the nearest 10 or 100.
- Mathematical Practices: MP.1 (make sense of problems & persevere), MP.3 (construct viable arguments & critique).
Success Criteria — Student Language
- I can write an equation with a letter for the unknown that matches the problem.
- I can solve a two-step problem and explain the order of my steps.
- I can estimate with rounding to check whether my answer is reasonable.
- I can show my thinking with a bar model or number line and justify my choice.