# Lesson 2

Explore Expressions and Sums

## Warm-up: Choral Count: Count to 41 (10 minutes)

### Narrative

### Launch

- “Count by 1, starting at 0.”
- Record as students count.
- Stop counting and recording at 41.

### Activity

- “What patterns do you see?”
- 1–2 minutes: quiet think time
- Record responses.

### Student Response

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### Activity Synthesis

- “Does anyone want to add an observation on why that pattern is happening here?”
- “Do you agree or disagree? Why?”

## Activity 1: Matching Dot Cards and Expressions (15 minutes)

### Narrative

The purpose of this activity is for students to relate dot images to addition expressions. In a previous activity, students discussed using addition expressions to show putting together the value of each dot cube. In this activity, students match expressions to dot images and find the total, either by using the dots in the image, or by finding the value of the expression. Students then create matching dot images and expressions by completing the missing component. When students match dot images and expressions and write expressions to match dot images, they reason abstractly and quantitatively (MP2).

### Launch

- Groups of 2

### Activity

- “In this activity, draw a line to connect each dot image to its matching expression. Then, find the total. On the second page, complete the missing expressions or the missing dot images.”
- 5 minutes: independent work time
- “Share your work with your partner.”
- 3 minutes: partner discussion

### Student Facing

Match each pair of dots to an expression. Then, find the total.

expression | total |
---|---|

\(3+2\) | |

\(4+2\) | |

\(5+3\) | |

\(6+4\) | |

\(4+3\) |

Draw the missing dots to match the expression. Then, find the total.

Expression: \(4+2\)

Total: ____________

Expression: \(5+2\)

Total: ____________

Expression: \(2+6\)

Total: ____________

Write the missing expression to match the dots. Then, find the total.

Expression: _____________________

Total: ____________

Expression: _____________________

Total: ____________

### Student Response

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### Activity Synthesis

- “How did you know which expression matched each set of dots?” (I counted the dots on the first dot cube and wrote the number underneath, then counted the dots on the second one and found the right expression. I knew the first one was four because it looked like a dot cube and then I counted the second one and then found the matching expression.)

## Activity 2: Introduce: Check it Off, Add within 10 (20 minutes)

### Narrative

The purpose of this activity is for students to learn a new center called Check it Off, Add within 10. In this activity, students are introduced to the term **sum**. They find the sum of two numbers in a way that makes sense to them and write addition expressions to represent the sum. Students choose two number cards in order to make each expression. Dot cubes can be used instead of number cards if students would benefit from being able to count the dots in order to find the total. If working with number cards, students may find the sum in any way that makes sense to them, such as using objects, fingers, drawings, or known facts.

Number Cards are provided as a blackline master. Students will continue to use these throughout the year. Consider copying them on cardstock or laminating them and keeping them organized to be used repeatedly.

*MLR8 Discussion Supports.*To give all students an opportunity for verbal output, and to support the transfer of new vocabulary to long-term memory, invite students to chorally repeat phrases that include the term, “sum” in unison, 1–2 times. For example, “The sum of 1 and 3 is 4.”

*Advances: Speaking, Listening*

*Engagement: Internalize Self-regulation.*Provide students an opportunity to self assess and reflect on their own progress. For example, check in with students, and invite them to share their thinking.

*Supports accessibility for: Social-Emotional Functioning, Conceptual Processing*

### Required Materials

Materials to Gather

Materials to Copy

- Check It Off Stage 1 Recording Sheet Grade 1
- Number Cards (0-10)

### Required Preparation

- Create a set of cards from the blackline master for each group of 2.

### Launch

- Groups of 2
- Give each group a set of cards, two recording sheets, and access to 10-frames and two-color counters.
- “We are going to learn a game called Check It Off. Let’s play a round together.”
- “First we take out all of the cards greater than five. We will not use those cards in this game. Now I am going to pick two number cards and find the sum of the numbers. The
**sum**is the total when adding two or more numbers.” - Choose two cards.
- “What is the sum of the numbers? How do you know?”
- 30 seconds: quiet think time
- 1 minute: partner discussion
- Share responses.
- “Now I check off the sum. What addition expression represents the sum of the numbers?”
- 30 seconds: quiet think time
- Share responses.
- “I record the expression on my recording sheet next to the sum. Now it’s my partner’s turn.”

### Activity

- “Take turns choosing two cards, finding the sum, and writing an addition expression. You may have more than one expression for each sum.“
- 10 minutes: partner work time
- Consider asking:
- “How did you find the sum?”
- “What expression did you write? What does the expression show?”

- Monitor for students who draw pictures or use fingers to find sums.

### Student Response

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### Activity Synthesis

- Display number cards 4 and 3.
- "How can we find the sum of these numbers?"
- Invite previously identified students to share.
- "What addition expression can we write to represent the sum of these numbers?" (\(4 + 3 = 7\) or \(3 + 4 = 7\))

## Lesson Synthesis

### Lesson Synthesis

**Math Community**

“Let’s revisit our mathematical community chart.”

Display the chart.

“Based on what we did today, what can we add to “Doing Math”?

## Cool-down: Expressions and Sums (5 minutes)

### Cool-Down

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