Dividing Fractions: Keep, Change, Flip
6-8
1
Adding Fractions with Different Denominators
Lesson Details
Grade Level
3-5
Duration (minutes)
2
Summary
A Grade 3-5 math lesson teaching a four-step process for adding fractions with different denominators — find a common denominator, rewrite each fraction, add the numerators, and simplify — with an explanation of why different denominators can't be combined directly, using 1/4 + 1/6 = 5/12 as the worked example.
Student Worksheet: Adding Fractions with Different Denominators
Teacher Note: Students can watch the video lesson above and answer the questions. Click the “Teacher Answer Key” dropdown below when you are ready to review the solutions!
Key Concepts:
• Why It Matters: The denominator tells the size of the pieces — different denominators mean different-sized pieces, so you can’t combine them directly.
• Step 1 & 2: Find a common denominator using multiples, then rewrite each fraction as an equivalent fraction with that denominator.
• Step 3: Add the numerators and keep the denominator the same — never add the denominators.
• Step 4: Simplify the answer if the numerator and denominator share a common factor greater than 1.
Instructions: Read each question carefully and write your answer in the space provided.
- Question 1: Why can’t you add 1/4 + 1/6 without finding a common denominator first?
- Question 2: Find the common denominator of 4 and 6 by listing multiples of each.
- Question 3: Rewrite 1/4 and 1/6 as equivalent fractions with a denominator of 12.
- Question 4: Add 3/12 + 2/12. What is the answer?
- Question 5: Can 5/12 be simplified? How do you know?
Click to reveal Teacher Answer Key
1. Because the denominators are different, the pieces (fourths and sixths) are different sizes and can’t be combined directly.
2. Multiples of 4: 4, 8, 12, 16. Multiples of 6: 6, 12, 18, 24. The smallest match is 12.
3. 1/4 × 3/3 = 3/12. 1/6 × 2/2 = 2/12.
4. 3/12 + 2/12 = 5/12.
5. No, because 5 and 12 do not share a common factor greater than 1, so 5/12 is already fully simplified.
Disclaimer: This worksheet was generated with AI assistance based on original video content. It is intended for educational reference only. Teachers are encouraged to review and adjust questions to fit their curriculum standards before classroom use.
🎯 Extension Activity: Add 1/3 + 1/5 using all four steps: find a common denominator, rewrite each fraction, add the numerators, and simplify if possible. Show every step.