Lesson 2

Estimating Sums

Est. Class Sessions: 2
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Mathematical Standards

2.NBT.A
Understand place value. (2.NBT.A.1)
2.NBT.B
Use place value understanding and properties of operations to add and subtract. (2.NBT.B.7, 2.NBT.B.8, 2.NBTB.9)
2.MD.B
Relate addition and subtraction to length. (2.MD.B.6)

Standards for Mathematical Practice

MP1.
Make sense of problems and persevere in solving them.
MP2.
Reason quantitatively.
MP3.
Construct viable arguments and critique the reasoning of others
MP4.
Model with mathematics.
MP5.
Use appropriate tools strategically.
MP6.
Attend to precision.
MP7.
Look for and make use of structure.

Students use their knowledge of place value to explore estimation of sums. They develop strategies for determining the reasonableness of a sum such as finding friendly numbers and adding hundreds.

Content in this Lesson

  • Showing and recognizing different partitions of multidigit numbers using different representations (e.g., base-ten pieces, number lines, number sentences) [E3].
  • Estimating sums using mental math strategies (e.g., rounding using benchmarks, using friendly numbers, composing and decomposing numbers, counting) [E8].
  • Knowing what is important to solve a problem [MPE1].
  • Finding an efficient strategy for solving a problem [MPE2].
  • Using estimation to check for reasonableness [MPE3].
  • Showing or telling how to solve a problem [MPE5].
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Materials for Students

Daily Practice and Problems Lesson Homework Assessment

Student Books

 Student Activity Book

Teacher Resources

 Teacher Guide - digital

Supplies for Student Pairs

set of base-ten pieces (2 packs, 11 flats, 20 skinnies, 21 bits)

Materials for the Teacher

Display of Open Number Lines Master from Lesson 1 (Teacher Guide)
Display of Setting Goals (Student Activity Book) Pages 719–720
Display of Closest Estimate Master (Teacher Guide)
Unit 14 Assessment Record
Display set of base-ten pieces (2 packs, 11 flats, 20 skinnies, 21 bits)
chart paper

Materials Preparation

Prepare Estimation Strategies for Addition Chart. List the strategies students used when estimating sums with two-digit numbers or use the chart from Unit 7:

  • Adding tens
  • Counting on by tens
  • Using friendly numbers
  • Using coins

During the lesson, estimation strategies for larger numbers will be added to the chart.

Assessment in this Lesson

Assessment Expectation Assessed Math Practices Expectation Assessed
Is it Reasonable
with Feedback Box
Student Activity Book
Pages 725–728
E8. 
Estimate sums and differences using mental math strategies (e.g., rounding using benchmarks, using friendly numbers, composing and decomposing numbers, counting).
MPE1. 
Know the problem. I read the problem carefully. I know the questions to answer and what information is important.
MPE2. 
Find a strategy. I choose good tools and an efficient strategy for solving the problem.
MPE3. 
Check for reasonableness. I look back at my solution to see if my answer makes sense. If it does not, I try again.
MPE5. 
Show my work. I show or tell how I arrived at my answer so someone else can understand my thinking.

Vocabulary in this Lesson