1st Grade · Operations & Algebraic Thinking
1.OA.B.4: Understand subtraction as an unknown-addend problem
1.OA.B.4 is a 1st grade Common Core math standard in Operations & Algebraic Thinking. 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 subtraction as an unknown-addend problem. For example, subtract 10 - 8 by finding the number that makes 10 when added to 8.
In plain words
Understand subtraction as an unknown-addend problem.
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
If 5 + 3 = 8, what is 8 - 3?
- 3
- 5
- 8
Where students can get stuck
- Counting backward for every problem, even 15 - 13, and losing track, landing on 3 or 1 instead of 2.
- Counting the starting number as a step, saying "8, 9, 10, that's 3" for 10 - 8 instead of 2.
- Treating 10 - 4 as a brand-new problem, without noticing that the well-known fact 6 + 4 = 10 already answers it.
Effective teaching strategies
- Ask “What do I add to 8 to get 10?” for 10 − 8, and have students build 8 with cubes and add on until they reach 10.
- Mark 13 and 15 on a number line and have students hop up from 13, counting only the hops, so 15 − 13 becomes a short count up.
- Show 6 + 4 = 10 and ask students to use it to answer 10 − 4 before they compute anything new.
Units that teach this standard
Find where 1.OA.B.4 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
Everyday Mathematics
i-Ready Classroom Mathematics
Illustrative Mathematics
Math Expressions
Reveal Math
Don’t see your curriculum? Contact Bobby and we’ll see if we can help!
Share it with families
Families can read Subtracting by finding the missing part for a plain-language look at this skill, with three questions to try together and ideas for helping at home.
Help every student practice problem solving 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.