Lesson 26: Adding & Subtracting Fractions (Unlike Denominators)

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• Lesson Description
• Learning Objectives
• Topics Covered
• Key Terms
• Lesson Examples
• Practice Problems
• Tips & Common Mistakes
• Summary
• Challenge Problems
• Unit Navigation

Lesson Description

This lesson teaches students how to add and subtract fractions with unlike denominators by finding a common denominator, converting fractions, performing the operation, and simplifying results.

Learning Objectives

• Understand the need for a common denominator when adding or subtracting fractions.
• Convert fractions to equivalent fractions with a common denominator.
• Add and subtract fractions with unlike denominators and simplify the results.

Topics Covered

• Identifying unlike denominators
• Finding the least common denominator (LCD)
• Converting to equivalent fractions
• Adding and subtracting fractions
• Simplifying the answer

Key Terms

• Unlike Denominators: Denominators that are not the same in two or more fractions.
• Least Common Denominator (LCD): The smallest number that is a multiple of each denominator.
• Equivalent Fraction: A fraction that has the same value as another fraction but a different numerator and denominator.

Lesson Examples

Example 1: Adding Fractions

1. Add 1/4 + 1/6.
2. Find the LCD of 4 and 6: 12.
3. Convert each fraction: 1/4 = 3/12, 1/6 = 2/12.
4. Add: 3/12 + 2/12 = 5/12.

Example 2: Subtracting Fractions

1. Subtract 5/8 - 1/3.
2. Find the LCD of 8 and 3: 24.
3. Convert: 5/8 = 15/24, 1/3 = 8/24.
4. Subtract: 15/24 - 8/24 = 7/24.

Practice Problems

1. Add 2/5 + 3/10.
2. Subtract 7/12 - 1/4.
3. Add 3/8 + 5/6.
4. Subtract 9/10 - 2/3.

Tips & Common Mistakes

• Always find the LCD before performing the operation.
• Convert both fractions to equivalent fractions with the common denominator.
• Don’t forget to simplify your final answer if possible.

Summary

Adding and subtracting fractions with unlike denominators requires finding a common denominator, converting fractions, performing the operation, and simplifying. Mastery of this skill is crucial for working with fractions in Pre-Algebra.

Challenge Problems

1. Add 7/9 + 2/5 and simplify your answer.
2. Subtract 11/12 - 3/8 and simplify your answer.
3. Create a word problem involving adding or subtracting fractions with unlike denominators.