CCSS.Math.Content.1.OA.D.8
The standard
Determine the unknown whole number in an addition or subtraction equation relating three whole numbers.
Common Core State Standards for Mathematics · Operations and Algebraic Thinking
What this standard means
Students need to find the missing number in an addition or subtraction equation, no matter where the blank is. They should understand that the equal sign means both sides have the same value, not just “the answer comes next.” They can use counting on, counting back, objects, drawings, number lines, or known facts.
Mastery looks like solving equations such as 9 + ? = 14, ? - 4 = 6, and 7 = 3 + ? with a clear strategy. Students often get stuck when the blank is before the equal sign or when they treat the equal sign as a signal to calculate only from left to right.
Ways to teach it
- Use ten-frames and counters to build 6 + ? = 10, then have students record the matching equation.
- Ask students to write or tell how they know the missing number in 12 = 8 + ? without guessing.
- Show four equations on whiteboards, and have students circle the one that is true after filling the blank.
- Connect to sharing snacks: “You have 5 crackers, need 9 total, how many more go on the plate?”
Plan a lesson for CCSS.Math.Content.1.OA.D.8
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Related standards
- CCSS.Math.Content.1.OA.A.1
Use addition and subtraction within 20 to solve word problems involving situations of adding to, taking from, putting together, taking apart, and comparing, wit...
- CCSS.Math.Content.3.OA.A.4
Determine the unknown whole number in a multiplication or division equation relating three whole numbers.
- CCSS.Math.Content.4.OA.A.3
Solve multistep word problems posed with whole numbers and having whole-number answers using the four operations, including problems in which remainders must be...
- CCSS.Math.Content.1.OA.A.2
Solve word problems that call for addition of three whole numbers whose sum is less than or equal to 20, e.g., by using objects, drawings, and equations with a ...