Curriculum  /  Math  /  2nd Grade  /  Unit 2: Adding and Subtracting Within 100  /  Lesson 8

Adding and Subtracting Within 100

Lesson 8

Math

Unit 2

2nd Grade

Lesson 8 of 21

Objective

Relate the standard algorithm for addition to other methods to add and explain thinking.

Student-Facing

I can solve addition problems vertically.

Common Core Standards

Core Standards

  • 2.NBT.B.5 — Fluently add and subtract within 100 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction.
  • 2.NBT.B.9 — Explain why addition and subtraction strategies work, using place value and the properties of operations. Explanations may be supported by drawings or objects.

Foundational Standards

  • 1.NBT.C.4
  • 1.NBT.C.5
  • 1.NBT.C.6
  • 1.OA.B.3
  • 1.OA.B.4

Criteria for Success

  1. Represent an addition problem using a place value drawing and show the solution in a vertical model with numbers aligned by place value. 
  2. Show addition by combining the addends starting with the ones and continuing on to the tens. 
  3. In situations where there are more than 9 ones, make a new ten and vertically show the new ten on the line.

Tips for Teachers

  • This is the first time students will be introduced to adding using the standard algorithm. Please note that students are not expected to be fluent with this strategy but can use this strategy to support their thinking. It is also not expected that students know or use the term "standard algorithm".
  • When discussing how to line up numbers in order to add or subtract them vertically, emphasize that units need to be lined up because one can only add or subtract like units (ones with ones and tens with tens), as opposed to saying that numbers need to be lined up from right to left. This is an important distinction since lining numbers up from right to left no longer works when students begin working with decimals in later grades (e.g., adding 6.4 and 2.08 would result in an incorrect sum if lined up from right to left).
  • When students are adding they are supporting their thinking with place value drawings so that they understand they are adding ones together and tens together and when appropriate, making a new ten. Be sure to be precise with units when discussing. For example, in 18 + 40 students should say they are adding 1 ten and 4 tens not simply 1 and 4. 

Lesson Materials

  • Optional: Base ten blocks (9 tens and 18 ones per student or small group)
  • Tens place value chart (one per student or small group) — These should be laminated or in page protectors to reuse
  • Sheet protectors (1 per student)
  • Dry erase marker (1 per student)

Warm Up

5-10 minutes

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Anchor Tasks

15-25 minutes

Problem 1

Lizbeth solved 20 + 54 using the place value drawing below. 

a.   How could she record and solve this problem vertically using numbers?

b.   Solve the two equations below using a place value chart and record your work vertically. 

  1. 12 + 37 =
  2. 34 + 42 =

Purpose

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Problem 2

Solve these two equations using a place value chart and then writing your problem vertically. In each problem, do you need to make a new ten? Why or why not? 

a.   49 + 23 = _____

b.   54 + 38 = _____

Purpose

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Problem 3

a.   Explain the mistake in the work shown below. Then solve using vertical form. Use a place value chart to support your answer. 

25 + 7 = 

 

b.   Solve the following problem to practice:     58 + 6 =

Purpose

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Problem 4

Explain the mistake in the work shown below. Then solve using vertical form. Use a place value chart to support your answer. 

58 + 26

Purpose

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Problem Set

15-20 minutes

Target Task

5-10 minutes

Solve vertically. Use a place value chart to show your thinking.

59 + 13 = _____

Did you have to make a new ten? Why or why not?

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

Use base ten blocks and place value drawings to represent subtracting within 100.

Lesson 9
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Lesson Map

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Topic A: Adding & Subtracting with Multiples of Ten

Topic B: Strategies for Adding within 100

Topic C: Strategies for Subtracting within 100

Topic D: Working within 100 and Categorical Data

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