4th Grade · Number & Operations - Fractions
4.NF.B.3: Add and subtract fractions with the same denominator, like 5/12 + 6/12
4.NF.B.3 is a 4th grade Common Core math standard in Number & Operations - Fractions. Here’s what it really covers, and how you can help your students learn it.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
The standard
Understand a fraction a/b with a > 1 as a sum of fractions 1/b. a. Understand addition and subtraction of fractions as joining and separating parts referring to the same whole. b. Decompose a fraction into a sum of fractions with the same denominator in more than one way, recording each decomposition by an equation. Justify decompositions, e.g., by using a visual fraction model. Examples: 3/8 = 1/8 + 1/8 + 1/8; 3/8 = 1/8 + 2/8; 2 1/8 = 1 + 1 + 1/8 = 8/8 + 8/8 + 1/8. c. Add and subtract mixed numbers with like denominators, e.g., by replacing each mixed number with an equivalent fraction, and/or by using properties of operations and the relationship between addition and subtraction. d. 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.
In plain words
Add and subtract fractions with the same denominator, like 5/12 + 6/12.
Sample questions from student practice
These questions from Bobby's Math Club are the kinds of questions your students will see. You can try answering them to see what a student might see.
Question 1 of 3
Which sum is equal to 4/5?
- 1/5 + 1/5 + 1/5
- 1/4 + 1/4 + 1/4 + 1/4
- 1/5 + 1/5 + 1/5 + 1/5
Where students can get stuck
- Adding the denominators too, writing 5/12 + 6/12 = 11/24, an answer smaller than one of the starting fractions.
- Subtracting the smaller fraction from the larger, so 3 1/4 − 1 3/4 comes out as 2 2/4 instead of 1 2/4.
- Thinking a fraction can never be more than 1, so 7/4 looks like a mistake rather than one whole and three fourths.
Effective teaching strategies
- Have students count 5 twelfths and 6 twelfths together as 11 twelfths, so they see the denominator names the size of the piece and stays the same.
- Show 7/4 as seven 1/4 pieces on a number line and have students group four of them into one whole, so it becomes 1 3/4.
- Model 3 1/4 − 1 3/4 by trading one whole for 4/4 to make 2 5/4, then check the answer, 1 2/4, by adding it back.
Units that teach this standard
Find where 4.NF.B.3 lands in the program you teach. Each unit has a guide written for families. Unit names and order vary between editions and districts, so your school’s own materials have the exact sequence.
Bridges in Mathematics
enVision Mathematics
Eureka Math²
Everyday Mathematics
i-Ready Classroom Mathematics
Illustrative Mathematics
Math Expressions
Don’t see your curriculum? Contact Bobby and we’ll see if we can help!
Share it with families
Families can read Adding and subtracting fractions and mixed numbers for a plain-language look at this skill, with three questions to try together and ideas for helping at home.
Help every student practice fractions at home
In Bobby's Math Club, students practice at just the right level, with a hint when they need one, a clear explanation after every question, and kid-friendly videos. Unlimited practice is free for every family.
See how it works for teachers
Written by Robert “Bobby” Barnett
Bobby is an award-winning math teacher, the author of Meet Every Learner’s Needs, and the father of two elementary-school math learners. He uses Bobby’s Math Club with his own kids a few times every week. Learn more or contact Bobby.