Lesson 9

Subtraction Strategies

Est. Class Sessions: 1
X

Mathematical Standards

1.OA.A
Represent and solve problems involving addition and subtraction. (1.OA.A.1, 1.OA.A.2)
1.OA.B
Understand and apply properties of operations and the relationship between addition and subtraction. (1.OA.B.3, 1.OA.B.4)
1.OA.C
Add and subtract within 20. (1.OA.C.6)
1.OA.D
Work with addition and subtraction equations. (1.OA.D.8)

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.

Students solve comparison problems presented in the story or found in the environment. They use addition strategies (making 10, using doubles, using ten) to solve related subtraction problems and then add new subtraction strategies to the Invented Strategies chart from Lesson 1.

Content in this Lesson

  • Representing subtraction using stories, drawings, diagrams, counters, number sentences, number lines, or ten frames [E2].
  • Solving word problems (e.g., compare) involving two whole numbers whose sum is between 10 and 20 [E3].
  • Using mental math strategies and reasoning strategies (e.g., using doubles, using ten, making ten) to solve addition problems with sums between 10 and 20 and the related subtraction problems [E5].
  • Using strategies that apply the properties of addition (e.g., turn-around, compose and decompose numbers) to solve addition and
    subtraction problems [E6].
  • Finding the unknown whole number in an addition or subtraction equation relating three whole numbers [E7].
  • Knowing what is important to solve a problem [MPE1].
  • Finding strategies to solve problems [MPE2].
  • Checking for reasonableness [MPE3].
  • Showing or telling how to solve problems [MPE5].

Daily Practice and Problems CC–DD

CC. 100 Cents

DD. Weather Problems

X

Materials for Students

Daily Practice and Problems Lesson Homework Assessment

Student Books
Student Activity Book

Teacher Resources

 Teacher Guide - digital

Supplies for Students Pairs

20 connecting cubes
desk number line (0–40)

Materials for the Teacher

Display of first page of Compare Two Groups (Student Activity Book) Pages 413–414
Unit 12 Assessment Record
How Many Blue Birds Flew Away?: A Counting Book with a Difference by Paul Giganti, Jr. or other book
20 connecting cubes
class number line (0–130)
Invented Strategies chart from Lesson 1
chart paper, optional

Materials Preparation

Prepare to Display a Problem. For summarizing the lesson, write the following problem on a chart or other display:

    There are 17 pencils and 9 crayons in a box. How many more pencils than crayons are in the box?

Assessment in this Lesson

Assessment Expectation Assessed Math Practices
Expectation Assessed

Use Strategies
with Feedback Box
Student Activity Book Pages 415–418
E2.
Represent addition and subtraction using stories, drawings, diagrams, counters, number sentences, number lines, or ten frames.
E3.
Solve word problems (e.g., join, separate/take away, part-whole, compare) involving two whole numbers whose sum is between 10 and 20.
E5.
Use mental math strategies and reasoning strategies (e.g., using doubles, using ten, making ten) to solve addition problems with sums between 10 and 20 and the related subtraction problems.
E6.
Use strategies that apply the properties of addition (e.g., turn-around, compose and decompose numbers) to solve addition and subtraction problems.
E7.
Find the unknown whole number in an addition or subtraction equation relating three whole numbers.
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.
MPE5.
Show my work. I show or tell how I arrived at my answer so someone else can understand my thinking.