Lesson 8

Subtraction Strategies

Est. Class Sessions: 2
X

Mathematical Standards

1.OA.A
Represent and solve problems involving addition and subtraction. (1.OA.A.1)
1.OA.B
Understand and apply properties of operations and the relationship between addition and subtraction. (1.OA.B.3)

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.
MP8.
Look for and express regularity in repeated reasoning.

Students explore using tools and addition and subtraction strategies to solve take-away, part-whole, and comparative subtraction problems. They play the game How Many in the Bag to develop the counting-up strategy. They practice using number lines to help find the solutions to subtraction problems.

Content in this Lesson

  • Representing subtraction using stories, pictures, diagrams, counters, number sentences, number lines, or ten frames [E2].
  • Making connections between different representations of quantities.
  • Using strategies that apply the properties of addition (e.g., turn-around, zero) to solve addition and subtraction problems [E4].
  • Solving word problems (e.g., separate/take away, part-whole, compare) involving two whole numbers whose answer is less than or equal to 10 [E6].
  • Subtracting using invented, counting (e.g., counting on, counting up, counting back), and reasoning (e.g., making ten, using ten, using doubles) strategies [E7].
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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 Students

20 connecting cubes or counters
desk number line (0–40)
paper bag (or opaque substitute)

Materials for the Teacher

Display of Math Practices (Student Activity Book) Reference
Unit 6 Assessment Record
chart paper
paper bag (or opaque substitute)
counters
class number line (0–130)
Display of the completed Sorting Mat chart showing sums 0–10 from Lesson 1

Materials Preparation

Prepare Subtraction Cards. Copy and cut out one set of subtraction cards for each student pair using the Subtraction Cards for Small Numbers 1–6 Masters. If possible, use heavy weight paper or card stock to make the cards. Bind or clip each set together.

Prepare Bags of Counters. Place 9 counters in a paper bag for class demonstration. Prepare a paper bag of 8 to 15 counters for each pair of students. Label the front of each bag with the number of counters in the bag.

Prepare Sorting Mats. For display, use the Sorting Mat Master to draw a large Sorting Mat on chart paper. See Figure 1. Each student pair will also need a sorting mat. Use the large Sorting Mat Master to make a sorting mat on 11-inch x 17–inch paper. To copy the mat from an 8.5-inch x 11-inch paper to 11-inch x 17-inch paper, increase the copy ratio to 130%.

Figure 1: A large sorting mat on chart paper for display

Assessment in this Lesson

Assessment Expectation Assessed Math Practices Expectation Assessed
Observe Game How Many in the Bag
Teacher Guide - digital
E7.
Add and subtract within 10 using invented, counting (e.g., counting on, counting up, counting back), and reasoning (e.g., making ten, using ten, using doubles) strategies.
How Many in the Bag Number Sentences
Student Activity Book
Page 155
E2.
Represent addition and subtraction using stories, drawings, diagrams, counters, number sentences, number lines, or ten frames.
E6.
Solve word problems (e.g., join, separate/take away, part-whole, compare) involving two whole numbers whose answer is less than or equal to 10.
At the Zoo
Check-In:
Questions 4–7
with Feedback Box
Student Activity Book
Pages
158–159
E2.
Represent addition and subtraction using stories, drawings, diagrams, counters, number sentences, number lines, or ten frames.
E4.
Use strategies that apply the properties of addition (e.g., turn-around, zero) to solve addition and subtraction problems.
E6.
Use strategies that apply the properties of addition (e.g., turn-around, zero) to solve addition and subtraction problems.
E7.
Add and subtract within 10 using invented, counting (e.g., counting on, counting up, counting back), and reasoning (e.g., making ten, using ten, using doubles) strategies.
MPE1.
Know the problem. I read the problem carefully. I know the questions to answer and what informtion 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.