Curriculum  /  Math  /  2nd Grade  /  Unit 5: Adding and Subtracting Within 1,000  /  Lesson 20

Adding and Subtracting Within 1,000

Lesson 20

Math

Unit 5

2nd Grade

Lesson 20 of 25

Objective

Relate subtraction with expanded form to the standard algorithm in situations with up to two decompositions of a ten or hundred.

Student-Facing

I can relate expanded form to vertical subtraction with up to two decompositions. 

Common Core Standards

Core Standards

  • 2.NBT.B.7 — Add and subtract within 1000, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method. Understand that in adding or subtracting three-digit numbers, one adds or subtracts hundreds and hundreds, tens and tens, ones and ones; and sometimes it is necessary to compose or decompose tens or hundreds.

Foundational Standards

  • 1.NBT.B.2
  • 2.NBT.A.1
  • 2.NBT.A.2

Criteria for Success

  1. Use the standard algorithm to solve subtraction situations with up to two decompositions and represent with place value drawings. 
  2. Rewrite the minuend in non-standard form so that there are more than 10 tens and ones to subtract when there are not enough in the original representation. 
  3. Connect expanded form algorithm to the standard algorithm to solve subtraction situations. 

Tips for Teachers

Students are not expected to have proficiency with the standard algorithm until the end of 4th grade so students should continue to support their standard algorithm work with place value drawings, especially with up to two decompositions as they build their conceptual understanding. 

Warm Up

5-10 minutes

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Anchor Tasks

15-25 minutes

Problem 1

a.   Ally and Juan started to solve 416 - 184 differently. Notice how they started to solve and finish their work. 

Ally

Juan 

$$ \begin{array}{cccccr} &\overset{300}{\cancel{400}} &+ &\overset{110}{\cancel{10}} &+ &6 \\ - \ \ \ &100 &+ &80 &+ &4 \\ \hline \end{array}$$

b.   How are Ally and Juan's methods similar? How are they different?

Purpose

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Problem 2

Show how you would solve by recording your thinking using a place value drawing and modeling the work of your drawing vertically.

a.   608 - 129 = _____

b.   838 - 65 = _____

Purpose

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Problem Set

15-20 minutes

Target Task

5-10 minutes

Find the difference by solving vertically and model with a matching place value drawing. 

a.   534 - 175 = _____

b.   800 - 396 = ____

Student Response

Additional Practice

Daily Word Problems, Warm Ups, and Center Activities are aligned to the content of the unit but not necessarily to the lesson objective, therefore feel free to use them anytime during your school day.

Word Problems and Fluency Activities

Next

Solve one-step word problems using strategies to solve within 100.

Lesson 21
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Lesson Map

A7CB09C2-D12F-4F55-80DB-37298FF0A765

Topic A: Adding with Mental Strategies

Topic B: Adding within 1,000

Topic C: Subtracting with Mental Strategies

Topic D: Subtracting within 1,000

Topic E: Story Problems and Explaining Addition and Subtracting Thinking

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