Unit Plan 10 (Grade 5 Math): Adding Fractions with Unlike Denominators
5th graders add fractions with unlike denominators using models and equivalent fractions to find common units, simplify results, and explain reasoning clearly.
Focus: Build common denominators using equivalent fractions; add proper and improper fractions with visual models (strips, area, number lines) and explain reasoning.
Grade Level: 5
Subject Area: Mathematics (Number & Operations—Fractions)
Total Unit Duration: 5 sessions (one week), 45–60 minutes per session
I. Introduction
Students move from adding like denominators to unlike denominators by first seeing why common units matter. Using fraction strips, area models, and number lines, they generate equivalent fractions to create a shared unit, then add and simplify. They handle sums greater than 1 by converting between improper fractions and mixed numbers, and justify choices for a least common denominator (LCD) to keep work efficient.
Essential Questions
- Why do we need a common denominator to add fractions?
- How do equivalent fractions help us create a shared unit?
- When is it helpful to use the least common denominator vs. any common denominator?
- How do we represent and explain fraction addition with models and words?
II. Objectives and Standards
Learning Objectives — Students will be able to:
- Generate equivalent fractions to create a common denominator (including LCD).
- Add proper and improper fractions with unlike denominators; rename results as mixed numbers when appropriate.
- Use visual models (strips/area/number lines) to represent and explain fraction addition.
- Simplify results and justify reasonableness with benchmarks (0, 1/2, 1, 2).
- Communicate steps and choices (why this denominator? how did the model show the sum?) with precise vocabulary.
Standards Alignment — CCSS Grade 5
- 5.NF.1: Add and subtract fractions with unlike denominators (including mixed numbers) by replacing given fractions with equivalent fractions to produce an equivalent sum with like denominators; use visual fraction models and equations to represent the problem.
- Mathematical Practices emphasized: MP.1 (persevere), MP.3 (justify/critique), MP.4 (model), MP.6 (precision), MP.7 (structure).
Success Criteria — Student Language
- I can find a common denominator (often the least one) using multiples.
- I can rewrite fractions as equivalent fractions with that denominator.
- I can add the numerators, keep the denominator, and simplify my answer.
- I can model my work and explain what each part means.
- I can rename an improper fraction as a mixed number and check if my answer makes sense.