Lesson 3

Is It Reasonable

Est. Class Sessions: 1–2
X

Mathematical Standards

2.NBT.B
Use place value understanding and properties of operations to add and subtract. (2.NBT.B.6, 2.NBT.B.8, 2.NBT.B.9)
2.MD.B
Relate addition and subtraction to length. (2.MD.B.6)
2.OA.A
Represent and solve problems involving addition and subtraction. (2.OA.A.1)

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.
MP5.
Use appropriate tools strategically.
MP6.
Attend to precision.

Students practice estimation skills, focusing on whether an answer makes sense. They estimate the answers to problems and explain how they determined their estimates.

Content in this Lesson

  • Estimating differences using mental math strategies (e.g., rounding using benchmarks, using friendly numbers, composing and decomposing numbers, counting on) [E5, MPE2].
  • Subtracting multidigit numbers using mental math strategies (e.g., composing and decomposing numbers, counting up) with number lines, 200 Charts, and base-ten pieces [E3].
  • Knowing what information is important in a problem [MPE1].
  • Using estimation to check for reasonableness [MPE3].
  • Checking calculations [MPE4].
  • Explaining how estimates were determined [MPE5].

Daily Practice and Problems I–J

I. Subtraction Practice: Group A

J. Coin Puzzle

X

Materials for Students

Daily Practice and Problems Lesson Homework Assessment

Student Books

 Student Activity Book

Teacher Resources

 Teacher Guide - digital

Supplies for Students

desk number line (0–100)
collection of coins (quarters, nickels, dimes, pennies)
base-ten pieces (21 bits, 20 skinnies, 5 flats)

Materials for the Teacher

Display of Math Practices (Student Activity Book) Reference
Display of They Need Your Advice Master (Teacher Guide)
Unit 9 Assessment Record
Subtraction Strategies Chart from Lesson 2
chart paper

Assessment in this Lesson

ASSESSMENT EXPECTATION ASSESSED MATH PRACTICES EXPECTATION ASSESSED
Pretzel Problem
with Feedback Box
Student Activity Book
Pages 451–452
E3.
Subtract multidigit numbers using mental math strategies (e.g., composing and decomposing numbers, counting up) with number lines, a 200 Chart, and base-ten pieces.
E5.
Estimate differences using mental math strategies (e.g., rounding using bench marks, using friendly numbers, compoing and decomposing numbers, counting on).
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.
MPE4.
Check my calculations. If I make mistakes, I correct them.
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