Topic 4: Subtraction Facts to 20: Use Strategies

Pacing (Duration of Unit): 9 Lessons

Desired Results

Transfer:
1. Makes sense of problems and persevere in solving them.
2. Reason abstractly and quantitatively.
3. Construct viable arguments and critique the reasoning of others.
4. Model with mathematics.
5. Use appropriate tools strategically.
6. Attend to precision.
7. Look for and make use of structure.
8. Look for and express regularity in repeated reasoning.
Established Goals:
  • 1.OA.1 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.
  • 1.OA.4 Understand subtraction as an unknown-addend problem. For example, subtract 10 – 8 by finding the number that makes 10 when added to 8.
  • 1.OA.5 Relate counting to addition and subtraction (e.g., by counting on 2 to add 2).
  • 1.OA.6 Add and subtract within 20, demonstrating fluency for addition and subtraction within 10. Use mental strategies such as counting on; making ten (e.g., 8 + 6 = 8 + 2 + 4 = 10 + 4 = 14); decomposing a number leading to a ten (e.g., 13 – 4 = 13 – 3 – 1 = 10 – 1 = 9); using the relationship between addition and subtraction (e.g., knowing that 8 + 4 = 12, one knows 12 – 8 = 4); and creating equivalent but easier or known sums (e.g., adding 6 + 7 by creating the known equivalent 6 + 6 + 1 = 12 + 1 = 13).

Student "I Can" Statements:

  • I can use different strategies for addition to solve word problems (within 20).
  • I can use an addition fact to help me solve a subtraction problem.
  • I can count to help me add and subtract.
  • I can add facts within 20.
  • I can subtract facts within 20.

Prerequisite Standards:

  • K.CC.2 Count forward beginning from a given number within the known sequence (instead of having to begin at 1).
  • K.OA.2 Solve addition and subtraction word problems, and add and subtract within 10, e.g., by using objects or drawings to represent the problem.
  • K.OA.3 Decompose numbers less than or equal to 10 into pairs in more than one way, e.g., by using objects or drawings, and record each decomposition by a drawing or equation (e.g., 5 = 2 + 3 and 5 = 4 + 1).
  • K.OA.4 For any number from 1 to 9, find the number that makes 10 when added to the given number, e.g., by using objects or drawings, and record the answer with a drawing or equation.
  • K.OA.5 Fluently add and subtract within 5.
Big Ideas:

Numbers and the Number Line
The set of real numbers is infinite and ordered. Whole numbers, integers, and fractions are real numbers. Each real number can be associated with a unique point on the number line.

Operation Meanings & Relationships
There are multiple interpretations of addition, subtraction, multiplication, and division of rational numbers and each operation is related to other operations.

Properties
For a given set of numbers there are relationships that are always true, called properties, and these are the rules that govern arithmetic and algebra.

Basic Facts and Algorithms
There is more than one algorithm for each of the operations with rational numbers. Some strategies for basic facts and most algorithms for operations with rational numbers, both mental math and paper and pencil, use equivalence to transform calculations into simpler ones.

Practices, Processes, and Proficiencies
Mathematics content and practices can be applied to solve problems.
Essential Questions:

  • What strategies can you use while subtracting?
Students will know...

  • When using a number line to subtract, you can count back the number of spaces you are subtracting or find the distance between two numbers.
  • Some subtraction facts can be simplified by making use of the numbers' relationships to 10.
  • The inverse relationship between addition and subtraction can be used to find subtraction facts; every subtraction fact has at least one related addition fact.
  • There are different ways to solve subtraction facts. Certain strategies may be easier to use for different facts.
  • Objects, drawings, and equations can help you solve different types of word problems.
  • Mathematicians know how to think about words and numbers to solve problems.


Vocabulary:
Fact family, related facts
Students will be skilled at...

  • Using a number line to subtract by counting on or counting back.
  • Making subtraction easier by making 10 to subtract.
  • Counting on to subtract using 10 as a landmark.
  • Making addition and subtraction facts using the same three numbers.
  • Using addition facts to find subtraction facts.
  • Explaining strategies used to solve subtraction problems.
  • Solving different types of addition and subtraction problems with unknowns in different positions.
  • Using reasoning to write and solve number stories.

Assessment Evidence

Performance Assessment:
Other Evidence:

Formative Assessments:

Learning Plan

Learning Activities:

4-1 When using a number line to subtract, you can count back the number of spaces you are subtracting or find the distance between two numbers.
4-2 Some subtraction facts can be simplified by making use of the numbers' relationships to 10.
4-3 Some subtraction facts can be simplified by making use of the numbers' relationships to 10.
4-4 The inverse relationship between addition and subtraction can be used to find subtraction facts; every subtraction fact has at least one related addition fact.
4-5 The inverse relationship between addition and subtraction can be used to find subtraction facts; every subtraction fact has at least one related addition fact.
4-6 The inverse relationship between addition and subtraction can be used to find subtraction facts; every subtraction fact has at least one related addition fact.
4-7 There are different ways to solve subtraction facts. Certain strategies may be easier to use for different facts.
4-8 Objects, drawings, and equations can help you solve different types of word problems.
4-9 Mathematicians know how to think about words and numbers to solve problems.
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