Unit Plan 29 (Grade 2 Math): Mixed Operations—Unknowns in All Positions

Focus: Write equations with a symbol for the unknown (use a letter like n); solve and check reasonableness using mental math and estimation.

Grade Level: 2

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

This week strengthens problem solving with unknowns in all positions (result, change, start) using addition and subtraction within 100. Students model situations, choose strategies, write equations with an unknown, and verify answers with estimation and mental math. Emphasis: accuracy first, then efficiency and clear recording.

Essential Questions

• How do I decide where the unknown belongs in my equation?
• Which strategy (make 10, count on/back, doubles, compensation) fits this problem best?
• How do I know my answer is reasonable?

II. Objectives and Standards

Learning Objectives — Students will be able to:

1. Represent one- and two-step word problems with equations using a letter (n) for the unknown.
2. Solve within 100 using mental math and written methods; explain and record precisely.
3. Use estimation (rounding, friendly numbers) to check for reasonableness.
4. Identify problem structures: result unknown, change unknown, start unknown.

Standards Alignment — CCSS Grade 2 (focus this week)

• 2.OA.1: Use addition/subtraction within 100 to solve one- and two-step word problems with unknowns in all positions.
• 2.NBT.5: Fluently add and subtract within 100 using strategies based on place value and properties of operations.
• Mathematical Practices: MP.1 (make sense & persevere) threaded; MP.6, MP.7, MP.8 supported.

Success Criteria — Student Language

• I can write an equation with an unknown (n) that matches the story.
• I can solve within 100 and explain my strategy.
• I can use estimation to show my answer is reasonable.