Explain why addition and subtraction strategies work, using place value and the properties of operations.

Cognitive Complexity Level: 1-Recall

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

  • Solve addition and subtraction problems using models, pictures, equations, and words.
  • Ask if answers are reasonable and make sense.
  • Compare their strategies to others used by students in the class.
  • Clearly explain to teachers and peers the strategies they used.

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

  • Select appropriate addition and subtraction problems for student to solve.
  • Provide ample wait time for students to solve problems using models, pictures, equations, and words.
  • Ask students to compare and clearly explain their strategies to their peers using precise math language.
  • Purposefully select examples and non-examples of student strategies to discuss whole group.

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

  • How do your base ten blocks represent what’s happening in the addition/subtraction problem?  
    • Sample answer that indicates understanding: “I have 4 tens rods and 7 ones cubes to represent the number 47. Then I add 3 more tens rods and 2 ones cubes to show 32 being added to 47.  Now I have 7 tens rods and 9 ones cubes, so 47 plus 32 equals 79.”
  • How could you use addition to help you solve a subtraction problem? 
    • Sample answer that indicates understanding: “I can use the think-addition strategy! I can start with the lesser number than add up to the greater number. That will give me the difference, or answer to the subtraction problem.”
  • How can you break apart the numbers by place value to help you add/subtract?
    • Sample answer that indicates understanding: “I know that I can break apart the numbers into hundreds, tens, and ones, and then I can just add the hundreds together, add the tens together, and add the ones together to find the sum.”

[divider] [/divider] Additional Resources:

Additional in depth content knowledge

Blog Post: Progression of Addition and Subtraction

Blog Post: Adding From Left to Right? What’s Up with That?

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

  

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

  • Before your child solves a subtraction problem, ask them to pause and think if they will have to use regrouping (or trading). Ask them to explain why or why not? Then have them use a model to solve and explain their strategy.
  • Create addition and subtraction equations for your child to solve using virtual base ten blocks or an open number line. Ask them to use math vocabulary to explain each step.
  • Task: Solve 164-39. Explain how you could use an open number line to find the difference. Ask your child to explain how they could use addition to solve and check their work.