Lesson Plan: Finding Common Denominators

In this fifth lesson of the Adding and Subtracting Fractions Unit, students will learn how to find common denominators, a critical skill for adding and subtracting fractions with unlike denominators. By understanding how to determine the Least Common Denominator (LCD), students will be better prepared to rewrite fractions as equivalent fractions with a shared denominator.

Students will:

• Understand why a common denominator is needed for fraction addition and subtraction
• Use the Least Common Multiple (LCM) to find a common denominator
• Convert fractions into equivalent fractions with common denominators
• Practice identifying common denominators using number patterns and multiplication
• Apply their knowledge to real-world fraction problems

Designed for grades 3-5, this lesson aligns with Common Core standards and builds on students’ prior understanding of factors and multiples. By mastering this skill, students will be well-equipped for upcoming lessons on adding and subtracting fractions with unlike denominators.

This is the fifth lesson in a ten-part unit on adding and subtracting fractions. Future lessons will focus on performing fraction operations using the skills developed in this lesson.

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