Unit 1.4: Subtraction within 20

Different situations suggest different subtraction strategies, such as counting back, thinking addition, or decomposing to ten. Different situations can result in the same difference. The expressions that represent situations with the same difference are equal. This relationship can be recorded with an equal sign.

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Unless otherwise noted, SFUSD Math Core Curriculum is licensed under the Creative Commons Attribution 4.0 International License

Teacher-facing pages are green

Student-facing pages are white

notes for teachers are in the speaker notes

New Learning:

Re-engagement:

In Kindergarten, students began to develop an understanding of subtraction as taking apart and taking from.

• They subtracted within 10 and represented their thinking in a variety of ways.
• They developed fluency with subtraction within 5.

Addition strategies from Units 1.1 and 1.3

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• Students represent and solve problems involving subtraction.
• Students subtract within 20 using the counting back, thinking addition, and decomposing to 10 strategies.
• Students use the number line, ten frame, and tape diagram to represent subtraction problems.
• Students begin to develop an understanding of the connection between addition and subtraction.
• Students understand the meaning of the equals and subtraction symbols.
• Students work toward fluency with subtraction facts within 10.

Students are introduced to comparison situations for the first time, with difference unknown problems. The numbers are kept between 0 and 10 during this introduction.

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Suggested Lesson Sequence

Week 1: Oct. 26 - 30

Students investigate the subtraction strategies of counting back on the number line and decomposition to 10 on a double ten frame.

Lesson 1: LS 1 Day 1&2 Seesaw Counting Back

Lesson 2: LS 1 Day 3 Seesaw Lesson 2: Making a 10

Lesson 3: LS 1 Day 4 Seesaw Lesson 3

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Week 2: Nov. 2 - 6

Lesson 4: Apprentice Task Seesaw Jada's Books

Students investigate subtraction as the inverse of addition by using the Think Addition strategy with doubles and doubles plus one. They use a tape diagram to represent the situations.

Lesson 5: LS 2 Day 2 Seesaw Doubles

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Week 3: Nov. 9 -13

Lesson 6: LS2 Day 3 Doubles +1

Lesson 7: Expert Task Seesaw Lesson 7 - Cookies

Continuing activity on Jamboard

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Week 4: Nov. 16 - 20

Lesson 8: LS 3 Day Seesaw Lesson 8 - Cookie Comparison

Lesson 9: Jamboard, Seesaw Lesson 9 - Favorite Cookie Comparison

Lesson 10 : Milestone Task - Seesaw Milestone - Pickles

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Synchronous and Asynchronous Teaching Options:

Synchro-

nous (live)

Asynchronous (time-delayed)

Technology Resources

• Minus Mission Subtraction Game: connect subtraction expressions with their difference by shooting the blobs

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• Cuisinaire Counting: Match the length of a given cuisinaire rod with smaller rods of different sizes.

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• Fruit Splat Number Line Subtraction: Match a subtraction equation to a number line representation

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• Georgia CCSS-M Standards videos is a website from the State of Georgia that includes videos of all the math content standards. For this unit, watch the video for 1.OA.5.

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• These Doubles Cards from I See Maths can be used as visual supports for students to make sense of and practice doubles within 10 and within 20.

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• Expert Task Cookie Monster 3-Act Task
• The Teaching Channel 3-Act Task Modeling Instructional Video

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• LS 3 Who Has More? Game Teams compare numbers on a ten-frame with numbers on dice.

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Student PDFs

1.4 Classwork .S. .C.

1.4 Homework .S. .C.

Data Routine

Objective: The Data Routine has both social and a math objectives:

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Social

• Students build community by sharing about themselves - their person, lives, interests, & preferences - learning about their classmate’s, finding and celebrating their similarities and differences
• Students build community by recognizing their shared environment (e.g. weather)

Math

• Students develop their understanding of categorical and measurement data (see progression of standards in the following slides and here) as they:
• Formulate questions
• Collect data
• Organize and display the data
• Analyze the data, and
• Interpret the results
• Students apply other important math ideas from all domains

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See the Data Routine slides for a description of how to incorporate this routine into your lessons.

Daily Routine: Number of Days in School

Objective: To build one-to-one correspondence, lay the foundation for an understanding of place value, and give students a concrete sense of the magnitude of numbers up to 180 and their relationship to the passage of time.

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See the Number of Days in School (Spanish) slides for a description of how to incorporate this routine into your lessons.

Daily Routine: Counting Routine

Objective: To provide students opportunities to count forward and backwards by various whole numbers and decimals, developing an understanding of patterns in counting, addition and subtraction (and later multiplication) and place value.

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See the Counting Routine slides for a description of how to incorporate this routine into your lessons.

Math Talks:Addition or Subtraction Dot Talks

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Objective: Students use the relationship between addition and subtraction to determine the sum or difference represented by the dots.

Description: These Math Talks are designed to help students become familiar with three related whole numbers. Students will see that parts can be added to find the total, or a part can be subtracted from the total to find one of the parts.

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Question: What do you see? What equation would match the picture? Could a subtraction equation match the picture?

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Math Talks:Addition or Subtraction Dot Talks

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What do you see?

What equation would match the picture?

Could a subtraction equation match the picture?

Dot Talk

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What do you see?

What equation would match the picture?

Could a subtraction equation match the picture?

Dot Talk

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What do you see?

What equation would match the picture?

Could a subtraction equation match the picture?

Dot Talk

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What do you see?

What equation would match the picture?

Could a subtraction equation match the picture?

Dot Talk

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What do you see?

What equation would match the picture?

Could a subtraction equation match the picture?

Dot Talk

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What do you see?

What equation would match the picture?

Could a subtraction equation match the picture?

Dot Talk

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Lesson 1: LS1 Day 1&2

Whole Class or Groups: Launch

• Act out the subtraction story situation on a number line
• Review addition strategies chart from Unit 3
• Compare counting on and counting back

Independent work: Explore Seesaw Counting Back

• Circle the number in the box on the number line
• Spin the spinner (return to Seesaw)
• Subtract that number on the number line
• Write an equation to match

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Students subtract 0, 1, and 2 from a given number and explore the number line.

Whole Class or Groups: Summarize

• Students may notice that the number doesn’t change when they add 0, that the sum is the number before on the number line when they subtract 1, or that they move back 2 numbers when they subtract 2. Ask students how they know. Core Math to Emphasize: Mathematical situations that require the subtracting of small quantities can be done by counting back. Pictures and equations can be used to represent the situation.

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Math Norms

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Errors are gifts that promote discussion.

Answers are important, but they are not the math.

Talk about each other’s thinking.

Ask questions until ideas make sense.

Use multiple strategies and multiple representations.

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SAN FRANCISCO UNIFIED SCHOOL DISTRICT

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Jada has 16 books on her bookshelf. She took 1 off the bookshelf to read.

Let’s act it out!

Jada has 16 books on her bookshelf. She took 1 off the bookshelf to read.

How many books are on the bookshelf now?

11 - 0 = ?

11 - 1 = ?

11 - 2 = ?

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Notice and Wonder...

Lesson 2: LS 1 Day 3

Whole Class or Groups: Launch:

• Remind students of the Make a Ten strategy they used for addition
• Ask them how they might use that strategy in subtraction.
• Tell students that today they are going to explore all the subtraction problems that will result in ten.
• Demonstrate how to play with a student partner.

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Independent work: Seesaw Lesson 2: Making a 10

• Pick a teen number and fill the Double 10-Frame with that many counters.
• Then cross out the amount that makes 10
• Write the subtraction equation that matches.

• Students use counters and a double ten frame to find all the subtraction facts to 10.

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Whole Class or Groups: Summarize:

• Create all the subtraction equations that make 10 and look for patterns

Core Math to Emphasize: Decomposing to make ten can make subtraction easier. The decomposition can be seen with a ten frame.

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Math Norms

27

Errors are gifts that promote discussion.

Answers are important, but they are not the math.

Talk about each other’s thinking.

Ask questions until ideas make sense.

Use multiple strategies and multiple representations.

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SAN FRANCISCO UNIFIED SCHOOL DISTRICT

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Make a 10 !

15

15 - 5 =10

12

12 - 2 =10

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• Pick a teen number and fill the Double 10-Frame with that many counters.
• Then cross out the amount that makes 10
• Write the equation

Subtraction Combinations that...

Make a 10 !

What patterns do you notice?

Lesson 3: LS 1 Day 4

Whole Class or Groups: Launch

• Review Subtraction Anchor Chart
• Demonstrate decomposing to make a 10 and then some more on the Double 10 Frame and with the number bond
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Independent work: Explore Seesaw Lesson 3

• Solve the subtraction equations with the Double 10 Frame
• Decompose the second number to make a ten
• Then subtract the remainder
• Complete the equations

Students solve subtraction problems that cross the decade by subtracting to 10 and then some more.

Whole Class or Groups: Summarize

• Complete the equations and share student work that highlights the strategy.
• Look for patterns with decomposing to make a 10

Core Math to Emphasize: Decomposing to make ten can make subtraction easier. The decomposition can be seen with a ten frame.

Math Norms

34

Errors are gifts that promote discussion.

Answers are important, but they are not the math.

Talk about each other’s thinking.

Ask questions until ideas make sense.

Use multiple strategies and multiple representations.

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SAN FRANCISCO UNIFIED SCHOOL DISTRICT

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14-8=

14-4=10

10-4=6

Subtracting to 10 and then some more.

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14 - 8

4

4

14 - 4 =10

10 - 4 = 6

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17- 9 =

7 2

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17 - 7 = 10

10 - 2 =

What patterns do you notice?

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17- 9 =

7 2

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17 - 7 = 10

10 - 2 =

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16 - 8 =

6 2

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16 - 6 = 10

10 - 2 =

15 - 6 =

5 1

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15 - 5 = 10

10 - 1 =

Lesson 4: Apprentice Task

Whole Class or Groups: Launch: 3 Read Protocol

• Notice and Wonder
• What’s the story about?
• Units and Quantities
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Independent work: Seesaw Jada's Books

• Solve the story problem on the Double 10 Frame and the Number Line
• Record the equation in the box,
• Record you strategy with the mic.

Students solve a subtraction word problem using a double ten frame or a number line.

Whole Class or Groups: Summarize: Use student examples or the slides provided to highlight different subtraction strategies.

Core Math to Emphasize: The numbers in a situation can determine which strategy to use for a solution. A number line can represent many strategies.

Math Norms

41

Errors are gifts that promote discussion.

Answers are important, but they are not the math.

Talk about each other’s thinking.

Ask questions until ideas make sense.

Use multiple strategies and multiple representations.

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SAN FRANCISCO UNIFIED SCHOOL DISTRICT

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Notice and Wonder...

Jada had 15 books on her bookshelf. By the end of the week she had read 6 more books.

1st Read

What is this story about?

Let’s act it out!

Jada had 15 books on her bookshelf.

By the end of the week, she had read 6 more books. How many books are on the bookshelf now?

2nd Read

What are the quantities in the situation?

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___ - ___ = ___

Jada had 15 books on her bookshelf.

By the end of the week, she had read 6 more books. How many books are on the bookshelf now?

___ - ___ = ___

Subtracting to 10 and then some more.

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15 - 6

1

5

15 - =10

10 - =9

1

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Lesson 5: LS 2 Day 1&2

Whole Class or Groups: Launch:

• Show students a couple of the doubles pictures and ask them what they learned about doubles in addition. Ask them how this might help them with subtraction.
• Demonstrate how to start with an even number and break it in half so both parts are the same. Find the double.

Independent work: Explore: Seesaw Doubles (Spanish)

1. Start with the number in the number bond

2. Build a train with that many cubes

3. Break it in to half (2 equal parts)

4. Record the numbers in the number bond and the equation

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• Students use linking cubes where a total is broken into two equal parts to explore how doubles addition facts can be used in subtraction.

Whole Class or Groups: Summarize:

• Review subtraction facts and look for patterns
• Represent some of the equations on a tape diagram
• Add think addition (doubles) to the subtraction strategies chart

Core Math to Emphasize: Subtraction is the inverse of addition. Knowledge of addition doubles can be used to solve subtraction situations. A tape diagram can represent the situation.

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Math Norms

52

Errors are gifts that promote discussion.

Answers are important, but they are not the math.

Talk about each other’s thinking.

Ask questions until ideas make sense.

Use multiple strategies and multiple representations.

​

SAN FRANCISCO UNIFIED SCHOOL DISTRICT

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Where is the double in this picture?

How many are in each half?

12

6 6

12 - 6 = 6

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6 - 3 = 3

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8 - 4 = 4

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10 - 5 = 5

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12 - 6 = 6

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14 - 7 = 7

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16 - 8 = 8

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What patterns do you notice?

6

?

12

12 - 6 =

6 + ? = 12

6 + 6 = 12

?

?

Total

__ - __ = ?

__ + ? = __

? + __ = __

Lesson 6: LS 2 Day 3

Whole Class or Groups: Launch: Math Talk

• Doubles plus 1 and plus 2 tape diagrams
• Connect addition strategies to subtraction and subtraction equations

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Independent work: Explore: Day 3 Tape Diagram Student .S. .C., SeesawDoubles +1

• Use your doubles +1 facts to build the number in the tape diagram with cubes
• Use the drawing tool to fill in the tape diagram
• Use the drawing tool to write a subtraction equation

• Students draw tape diagrams to represent Think Addition problems with doubles +1.

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Whole Class or Groups: Summarize

• Review subtraction facts and look for patterns
• Represent some of the equations on a tape diagram
• Add think addition (doubles) to the subtraction strategies chart

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Core Math to Emphasize: Subtraction is the inverse of addition. Knowledge of doubles +1 can be used with addition to solve subtraction situations. A tape diagram can represent the situation.

Math Talk

6

6+1

13

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13 - 6 = 7

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or 13 - 7 = 6

Subtraction equations:

6

6+2

14

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14 - 6 = 8

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14 - 8 = 6

Subtraction equations:

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11 - ? = ?

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13 - ? = ?

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15 - ? = ?

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17 - ? = ?

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19 - ? = ?

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What patterns do you notice?

?

?+1

?

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__- __= __

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or __- __ = __

Subtraction equations:

Lesson 7: Expert Task

Whole Class or Groups: Launch: Three Act Task

• Act 1: Watch video: Notice and Wonder
• Act 2: Come up with a question and provide additional

Information

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Independent work: Explore: Seesaw Lesson 7 - Cookies

https://gfletchy.com/the-cookie-monster, Cookies in a Whole Package BLM, Cookies Left BLM

Cookies Eaten BLM

• Student determine How many cookies did the cookie monster eat?

using a tape diagram and number line.

Students determine how many cookies the Cookie Monster ate.

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Whole Class or Groups: Summarize

• Act 3: Reveal the answer
• Highlight the subtraction strategies counting back and counting on, on the number line
• Relate the missing numbers to subtraction and addition, if students are ready.

Core Math to Emphasize: Real-life problems can be solved with subtraction. Subtraction is the inverse of addition. Knowledge of addition strategies can help to solve subtraction situations. A tape diagram or a number line can represent the situation.

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This task includes Take From - Change Unknown situations which is new.

What’s your favorite

kind of cookie?

Act 1: Notice and Wonder...

Cookie Monster

Act 2

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How many cookies are left in the tray?

Act 2

How many cookies did I eat?

Pg.1

16

16

Pg.2

Act 3

16

- ? =

Subtraction equation:

Cookies left Cookies eaten

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16 - ? = 9

9 + ? = 16

?

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16

- ? =

Subtraction equation:

Cookies left Cookies eaten

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- ? =

• ? =

?

16

- ? =

Subtraction equation:

Cookies left Cookies eaten

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- ? =

• ? =

?

Write and solve your own Cookie Monster problems.

Lesson 8: LS 3 day 1

Whole Class or Groups: Launch: Show students the Cookies Left BLM from the Expert Task. Remind students of the quantities in the picture. Make a chart of the quantities if needed.Ask which row had the most left and how they know. Ask if we can figure out the difference between the number of cookies in each row.

Independent work: Explore: Cookie Comparisons .S. .C. Seesaw Lesson 8 - Cookie Comparison

• Students use the number of cookies left in each row to compare which row has more.
• Find the difference on each page
• Record your thinking with the mic “Row ___ has ___ more/less then row ___”
• Tell students they may use counters to represent the cookies in each row if they like.

Students solve comparison problems using the information from the Cookie Monster problem.

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Whole Class or Groups: Summarize Share two to three student examples. Be sure to show some that line up the quantities in the rows. Have students explain how they know what is the same and what is different about the rows. Relate the comparisons to tape diagrams and equations.

Core Math to Emphasize: Quantities can be compared and the difference can be determined using subtraction.

Write and solve your own Cookie Monster problems.

Cookies Left

Row 1

Row 2

Row 3

Cookies Left

Row 1

Row 2

Row 3

Cookie Comparison

Row ___ has more/less cookies than row ___ .

What is the difference between the two rows?

Pg.1

16

Notice and Wonder...

1

3

2

11

10

9

8

7

6

5

4

1

2

3

4

5

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9

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6

7

8

?

11 - 9 = ? 9 + ? =11

9

11

Row 1

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Row 2

Which row has more cookies left?

What is the difference?

9 - 6 = ? 6 + ? =9

9

6

Row 1

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Row 3

Which row has more cookies left?

What is the difference?

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?

11 - 6 = ? 6 + ? =11

11

6

Row 2

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Row 3

Which row has more cookies?

What is the difference?

Lesson 9: LS 3 day 3

Whole Class or Groups: Launch: Notice and Wonder pictograph

Students do a poll on Jamboard, voting for 1 of 3 types of favorite cookies

Organize the Jamboard pictograph and present a screenshot of the student data. Have students notice and count the votes for each type of cookie.

How many students voted? Which one had the most...the least?

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Independent work: Explore: Number Comparisons .S. .C. Number Comparisons with Equations .S. .C. Seesaw Lesson 9 - Favorite Cookie Comparison

Students use the Jamboard data to figure out the difference between the quantities of each cookie and record it. Students then tell how many more or fewer of each number.

Students use data and represent a comparison between two numbers with a tape diagram and find the difference using subtraction.

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Whole Class or Groups: Summarize Share student work or use the slides as a template to compare the data with a tape diagram and an equation.

Core Math to Emphasize: Quantities can be compared and the comparison can be represented with a tape diagram and an equation. Subtraction can be used to solve the problem.

Notice and Wonder...

What’s your favorite

kind of cookie?

Sprinkles Gingerbread Chocolate Chip

Screenshot of Jamboard data

16

16

?

Equation:

Sprinkles

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Gingerbread

Which cookie has more? Which has less?

What is the difference?

?

Equation:

Sprinkles

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Chocolate Chip

Which cookie has more? Which has less?

What is the difference?

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Equation:

Gingerbread

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Chocolate Chip

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Which cookie has more? Which has less?

What is the difference?

Milestone Task

Whole Class or Groups: Launch - 3 Read Protocol

• Notice and Wonder
• What’s the story about?
• What are the units and quantities?
• Remind students of all their addition and subtraction strategies.

Independent work: Seesaw Milestone - Pickles, Pickles BLM .S. .C., Pickles Three Read BLM .S. .C., Pickles Three Read Picture BLM

Students work to solve the “Min Loves Pickles” problem

They show their thinking with a math drawing and an equation.

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Students solve a word problem involving subtraction and decide which strategy to use to solve it.

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Whole Class or Groups: Pickles Answer Guide Teacher Pickles Rubric Teacher.

Look for student’s current understanding of the core math: The situation will determine the best strategy to use for subtracting two numbers. Strategies to consider are counting on or counting back, using doubles or, decomposing to make a 10, or using known facts. Core math: Some real-life situations can be solved with subtraction. The strategy used to solve the problem depends on the numbers involved.

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Notice and Wonder...

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What is this story about?

1st Read

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What are the quantities in the situation?

2nd Read

Min loves pickles. There were 17 pickles in a jar. Min ate 9 for a snack.

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Min loves pickles. There were 17 pickles in a jar. Min ate 9 for a snack.

How many pickles were left in the jar?

Show your thinking with a math drawing on Pg. 1 and write the equation on Pg. 2

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Pickles

Look for student’s current understanding of the core math: The situation will determine the best strategy to use for subtracting two numbers. Strategies to consider are counting on or counting back, using doubles or, decomposing to make a 10, or using known facts.

Use the Milestone task as formative assessment to determine potential areas for re-engagement during the next unit.Pickles Answer Guide Teacher Pickles Rubric Teacher.

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