# Adding and Subtracting Within 20

Students extend their knowledge of addition and subtraction within 20 to fluently add and subtract within 20 using various strategies. This work is put into practice as students solve familiar word problem types using tape diagrams and equations to represent what is happening mathematically.

Math

Unit 1

## Unit Summary

This introductory unit helps set students up for the major work of fluently adding and subtracting within 20 which is the end-of-year goal. By reviewing, building, and refining strategies for fluently adding and subtracting mentally, this will help students as they work flexibly with larger numbers in later units. Topic A re-engages students with their fluency within 10 which was the end-of-year goal of first grade and continues on their counting work extending from 120 to 200. Topic B allows students to use advanced strategies to add and subtract flexibly within 20. They use strategies such as make a ten to add, relate addition and subtraction to subtract by using known facts and making a ten strategies, subtracting by going down over ten, and converting to easier problems using known and doubles facts. In Topic C students re-engage with story problems and use tape diagrams to represent the math of the mathematical situations while focusing on adding to and taking from, and putting together and taking apart situation types.

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## Assessment

The following assessments accompany Unit 1.

### Mid-Unit

Have students complete the Mid-Unit Assessment.

### Post-Unit

Use the resources below to assess student understanding of the unit content and action plan for future units.

Expanded Assessment Package

Use student data to drive instruction with an expanded suite of assessments. Unlock Mid-Unit Assessments and Answer Keys to help assess progress with unit content and inform your planning.

## Unit Prep

### Intellectual Prep

#### Intellectual Prep for All Units

• Read and annotate "Unit Summary" and "Essential Understandings" portion of the unit plan.
• Do all the Target Tasks and annotate them with the "Unit Summary" and "Essential Understandings" in mind.
• Take the Post-Unit Assessment.

#### Unit-Specific Intellectual Prep

Read the following table that includes models used in this unit..

 number bond A number bond for 10 = 3 + 7 tape diagram Example: Armando buys 16 peppers for a barbeque. 7 of the peppers are red and the rest of the peppers are orange. How many orange peppers did Armando buy? ten frame Two ten frames showing 8 + 11

### Essential Understandings

• The number sequence can be extended beyond 120 by continuing the count by ones and by tens.
• Basic tens facts can be used to to support adding and subtracting within 20.
• Thinking of addition when subtracting can be a supportive strategy for fluently and flexibility subtracting within 20.
• Number bonds can be used to show relationships within numbers as students use make ten strategies to add and subtract.
• Making sense of problems and persevering in solving them is an important practice when solving word problems. Representing word problems with mathematical drawings, including tape diagrams, helps students model their thinking and helps them toward solutions.

### Materials

• Optional: Number Bond Template (1 per student) — These can be laminated or in page protectors to reuse
• Tens Frame Template (1 per student) — These can be laminated or in page protectors to reuse
• Linking cubes (2 different color towers of 10 per student)
• Blank Hundreds Chart (1 per student)
• Optional: Dry erase marker (1 per student) — Can continue to be used past Unit 1 for story problems but will not be referred to
• Optional: White board (1 per student) — Can continue to be used past Unit 1 for story problems but will not be referred to
• Optional: Manipulatives (As needed) — At teacher discretion on types used and how much are needed. Can continue to be used past Unit 1 for story problems but will not be referred to

## Unit Practice

Word Problems and Fluency Activities

Help students strengthen their application and fluency skills with daily word problem practice and content-aligned fluency activities.

## Lesson Map

Topic A: Adding and Subtracting within 10 and Counting

Topic B: Strategies to Add and Subtract within 20

Topic C: Story Problems within 20

## Common Core Standards

Key

Major Cluster

Supporting Cluster

### Core Standards

#### Number and Operations in Base Ten

• 2.NBT.A.2 — Count within 1000; skip-count by 5s, 10s, and 100s.

#### Operations and Algebraic Thinking

• 2.OA.A.1 — Use addition and subtraction within 100 to solve one- and two-step word problems involving situations of adding to, taking from, putting together, taking apart, and comparing, with unknowns in all positions, e.g., by using drawings and equations with a symbol for the unknown number to represent the problem.
• 2.OA.B.2 — Fluently add and subtract within 20 using mental strategies. By end of Grade 2, know from memory all sums of two one-digit numbers. See standard 1.OA.6 for a list of mental strategies.

• 1.NBT.B.2
• 1.NBT.C.5
• 1.NBT.C.6
• K.NBT.A.1

• 1.OA.A.1
• 1.OA.B.4
• 1.OA.C.5
• 1.OA.C.6
• K.OA.A.3
• K.OA.A.4

• 2.NBT.A.1
• 2.NBT.B.5

• 4.NF.B.3

• 3.OA.A.1
• 3.OA.A.3
• 3.OA.D.8
• 3.OA.D.9

### Standards for Mathematical Practice

• CCSS.MATH.PRACTICE.MP1 — Make sense of problems and persevere in solving them.

• CCSS.MATH.PRACTICE.MP2 — Reason abstractly and quantitatively.

• CCSS.MATH.PRACTICE.MP3 — Construct viable arguments and critique the reasoning of others.

• CCSS.MATH.PRACTICE.MP4 — Model with mathematics.

• CCSS.MATH.PRACTICE.MP5 — Use appropriate tools strategically.

• CCSS.MATH.PRACTICE.MP6 — Attend to precision.

• CCSS.MATH.PRACTICE.MP7 — Look for and make use of structure.

• CCSS.MATH.PRACTICE.MP8 — Look for and express regularity in repeated reasoning.

Unit 2

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