Standard

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 = _.

Student Language:

• "I can figure out what a missing number is in an addition or subtraction problem."

Explanation

About the Math, Learning Targets, and Rigor

This standard extends the work that students do in 1.OA.4 by relating addition and subtraction as related operations for situations with an unknown.

Examples of possible student “think-throughs”:

• 8+? = 11: “8 and some number is the same as 11. 8 and 2 is 10 and 1 more makes 11. So the answer is 3.”
• 5 =? −3: “This equation means I had some cookies and I ate 3 of them. Now I have 5. How many cookies did I have to start with? Since I have 5 left and I ate 3, I know I started with 8 because I count on from 5. . . 6, 7, 8.”

All students need to show a representation of the problem and communicate and justify their thinking

Resources

Videos

• Khan Academy
  • Scroll to 1.OA.8, click on skill, find videos on left side of each skill

Extra Practice

• North Carolina Tasks
• Illustrative Math Tasks
• Howard County Tasks
  • Click on 1st grade at bottom, then 1.OA.8
• Common Core Sheets