Unit Plan 22 (Grade 4 Math): Add/Subtract Like Denominators
Add & subtract fractions/mixed numbers with like denominators; solve word problems using models, equations, regrouping, and units with clear reasoning and checks for reasonableness.
Focus: Add and subtract fractions and mixed numbers with like denominators; represent and solve word problems with clear models, equations, and units.
Grade Level: 4
Subject Area: Mathematics (Number & Operations—Fractions)
Total Unit Duration: 5 sessions (one week), 45–60 minutes per session
I. Introduction
Students build on unit-fraction understanding to fluently add and subtract fractions that share the same denominator, including mixed numbers. They explain what each part means, keep the whole consistent, and record work with visual fraction models, number lines, and equations featuring an unknown. Word problems highlight reasonableness and units.
Essential Questions
- Why do we add/subtract numerators (not denominators) when denominators are the same?
- How do models (area, strips, number line) and equations show the same whole and the same unit?
- What strategies help when subtracting mixed numbers (e.g., regrouping a whole into unit fractions)?
II. Objectives and Standards
Learning Objectives — Students will be able to:
- Add and subtract fractions with like denominators using models and equations.
- Add and subtract mixed numbers with like denominators, including regrouping when necessary.
- Represent and solve word problems with diagrams, number lines, and equations with a symbol for the unknown.
- Explain solutions with precise units, correct labels, and reasonableness checks.
- Use academic vocabulary (e.g., unit fraction, denominator, regroup, decompose/compose, equivalent) to justify steps.
Standards Alignment — CCSS Grade 4
- 4.NF.3c: Add and subtract mixed numbers with like denominators (e.g., by replacing each mixed number with an equivalent fraction and/or by regrouping to produce an equivalent mixed number).
- 4.NF.3d: Solve word problems involving addition and subtraction of fractions referring to the same whole and having like denominators, e.g., by using visual fraction models and equations to represent the problem.
Success Criteria — Student Language
- I can add/subtract fractions with the same denominator and explain why the denominator stays the same.
- I can add/subtract mixed numbers and regroup a whole into unit fractions when needed.
- I can solve a word problem with a model and an equation and check if my answer makes sense with units.