CCSS.Math.Content.1.OA.B.4
The standard
Understand subtraction as an unknown-addend problem.
Common Core State Standards for Mathematics · Operations and Algebraic Thinking
What this standard means
Students need to see a subtraction problem as a missing part in an addition problem. For 9 minus 6, they should think, “6 plus what makes 9?” They should use objects, drawings, ten-frames, number lines, and equations to connect the two facts.
Mastery looks like choosing addition to solve subtraction, not just counting backward every time. Students can explain the missing number and write a matching equation. Common sticking points are mixing up the total and the parts, counting the starting number by mistake, and not seeing that 6 + 3 = 9 matches 9 - 6 = 3.
Ways to teach it
- Give partners 10 counters and subtraction cards, then have them build the total and find the missing addend with a different color.
- Ask students to explain in writing: “How can 7 + ___ = 12 help you solve 12 - 7?”
- Show 8 - 5 and ask students to write the matching addition sentence on a whiteboard in 20 seconds.
- Use a snack count: “We have 10 crackers and 6 are on the plate, how many are still in the bag?”
Plan a lesson for CCSS.Math.Content.1.OA.B.4
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Related standards
- CCSS.Math.Content.1.OA.B
Understand and apply properties of operations and the relationship between addition and subtraction.
- CCSS.Math.Content.1.OA.D.8
Determine the unknown whole number in an addition or subtraction equation relating three whole numbers.
- CCSS.Math.Content.2.OA.A
Represent and solve problems involving addition and subtraction.
- CCSS.Math.Content.K.OA.A
Understand addition as putting together and adding to, and understand subtraction as taking apart and taking from.