Determine the unknown whole number in an addition or subtraction equation relating three whole numbers. For example, determine the unknown number that makes the equation true in each of the equations 8 + ? = 11, 5 = _ – 3, 6 + 6 = _.



Click here to learn about the process used to unpack the standards and create learning targets.

Unpacking the Standard: 1.OA.D.8
Student Friendly Learning Target: 1.OA.D.8


Students are expected to solve for an unknown portion in an equation, regardless of its position in that equation. Additionally, students are to be familiar with that unknown portion being represented as a symbol, empty space, question mark or shape. The students’ previous understanding of the equal sign will enhance their ability to demonstrate an understanding of this missing portion equation.

Understanding the Standard:

    • Fact families are a wonderful strategy in helping students to relate addition and subtraction to one another. Additionally, teachers should guide students to the understanding that if a student knows that 2 + 3 = 5, then they can use that knowledge to solve 5 = ? + 2.
    • Helping students to master the process of using subtraction to find the missing addend as well as using addition to find the missing portion in a subtraction problem will assist in students’ ability to fluently solve these problems.
    • The use of manipulatives, technologies, models, and drawings can aid in helping students to visualize the unknown portion in an algebraic problem.

      Questions to Focus Instruction:

        • Do students understand that addition and subtraction are related to one another?
        • Can students reason and communicate how to solve for an unknown portion in a number sentence?
        • Can students explain the role the equal sign plays in algebraic equations in that they understand that both sides of the equal sign must have identical values?


          Prior to: Students can add and subtract fluently through 10. Students have demonstrated knowledge that addition involves “adding to” and subtraction involves “taking away”.

          At Grade Level:
          Students can add and subtract fluently. They demonstrate understanding that addition and subtraction facts are related to one another and the equal sign indicates equality in a number sentence.

          Moving Beyond:
          Students will build upon their existing knowledge and apply this standard to word problems. They can take information in a word problem and correctly write a number sentence with an unknown portion and solve accordingly. Go to 3.OA.B.6 to see the progression of related skills.