Understand subtraction as an unknown-addend problem. For example, subtract 10 – 8 by finding the number that makes 10 when added to 8.

Cognitive Complexity Level: 1-Recall

[divider] [/divider] Students are able to… 

  • represent related addition and subtraction facts using objects, pictures or words
  • use vocabulary such as addends, missing addend and total
  • explain their thinking based on relationship between addition and subtraction

[divider] [/divider] Students are able to…because teachers:

  • provide opportunities to explore problems with missing addends in all locations
  • model use of vocabulary relating to addends
  • ask questions and use tasks that support discussions about the connection between addition and subtraction

 [divider] [/divider] Questions to ask students:

  • Ask:  What strategy did you use to determine the unknown?
    • Sample answer that indicates understanding: Student can explain how they solved the problem by adding/counting up to find the answer (think addition to subtract) or rewrite the subtraction equation as an addition sentence to make it easier to solve.
  • Ask: How did you use addition to solve the subtraction problem?  
    • Sample answer that indicates understanding: Student explains how they can rewrite the subtraction equation as an addition equation.  Student explains how the represented the missing addend – question mark or a box.

[divider] [/divider] Additional Resources:

Additional in depth content knowledge

Video: Georgia Standards 1.OA.2.4

Video: Understand that Subtraction can be thought of as an Unknown Addend Problem

https://learnzillion.com/lesson_plans/3381

[divider] [/divider] Sample Formative Assessment Tasks:

[divider] [/divider] Resources/Tasks to Support Your Child at Home:

    • Play a game using half of a plastic egg and some sort of small objects like beans.  Put some beans on the table and have your child count them.  Then hide some of the beans under the egg.  Have him/her write an addition and a subtraction problem to match what happened. 
    • Rewrite addition equations as related subtraction equations 
    • Rewrite addition equations as subtraction equations with a missing addend: What goes with this part to make the total?