CCSS.Math.Content.1.OA.A.1
The standard
Use addition and subtraction within 20 to solve word problems involving situations of adding to, taking from, putting together, taking apart, and comparing, with unknowns in all positions, e.g., by using objects, drawings, and equations with a symbol for the unknown number to represent the problem.
Common Core State Standards for Mathematics · Operations and Algebraic Thinking
What this standard means
Students need to solve story problems with totals and differences up to 20. They should act out the story, draw it, or write an equation. The unknown might be the start, the change, or the result, so they need to make sense of the situation before choosing addition or subtraction.
Mastery looks like matching the story to a model and equation, then explaining what the unknown means. Students often get stuck when the missing number is not at the end, such as “Some birds were in a tree, 5 flew away, and 7 are left.” They may also grab numbers and add without thinking about the action.
Ways to teach it
- Use counters and a cup to act out start unknown, change unknown, and result unknown stories within 20.
- Ask students, “What is happening in the story, and what does the missing number stand for?” before they solve.
- Give one word problem and have students show it with a drawing, an equation, and a boxed unknown.
- Use a class snack count, such as crackers eaten and crackers left, to write and solve a subtraction story.
Plan a lesson for CCSS.Math.Content.1.OA.A.1
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