# Lesson 9

## Warm-up: Number Talk: Ten and Some More (10 minutes)

### Narrative

The purpose of this Number Talk is to elicit strategies and understandings students have for making a ten when adding a one-digit number to three-digit numbers. In the synthesis, the focus is on how students look for ways to make ten. These understandings help students develop fluency and will be helpful in the lesson as students add 2 three-digit numbers and consider composing units.

### Launch

• Display one expression.
• “Give me a signal when you have an answer and can explain how you got it.”
• 1 minute: quiet think time

### Activity

• Keep expressions and work displayed.
• Repeat with each expression.

### Student Facing

Find the value of each expression mentally.

• $$528 + 2$$
• $$528 + 7$$
• $$487 + 3$$
• $$487 + 8$$

### Student Response

For access, consult one of our IM Certified Partners.

### Activity Synthesis

• “What do you notice about the sums?” (I made a ten to find the sum. They all show adding some ones to three-digit numbers. There’s a pattern in the ones—0 ones, 5 ones, 0 ones, 5 ones.)
• “Why are $$528 + 2$$ and $$487 + 3$$ helpful in finding the value of the other expressions?” (We know they make a new ten, so it helped me think about how I could decompose a number to help make a ten.)

## Activity 1: How Did You Add Three-digit Numbers? (20 minutes)

### Narrative

The purpose of this activity is for students to practice adding within 1,000 with an emphasis on adding by place. Throughout the activity, students have opportunities to explain their methods and representations to peers. In the synthesis, students have opportunities to question and critique the work of their peers as they compare different methods for adding three-digit numbers and different representations that show composing units when adding by place (MP3).

This activity uses MLR8 Discussion Supports. Advances: conversing

Engagement: Provide Access by Recruiting Interest.Provide choice. Invite students to decide which problem to start with and the strategy they feel most comfortable solving with.
Supports accessibility for: Social-Emotional Functioning, Organization, Attention

### Required Materials

Materials to Gather

• Groups of 2

### Activity

• “We are going to practice adding 2 three-digit numbers. You can find the value of each sum in any way that makes sense to you. After some time working independently, you can continue working with a partner.”
MLR8 Discussion Supports
• Display sentence frames to support students when they explain their strategy:
• “First, I _____ because . . .”
• “I noticed _____ so I . . .”
• 5 minutes: independent work time
• 4 minutes: partner work time
• “Choose one expression and share how you found the value of the sum with a new partner.”
• 3 minutes: partner discussion
• Monitor for students who use base-ten blocks, base-ten diagrams, or other representations that clearly show adding by place.

### Student Facing

Find the value of each expression. Show your thinking.

1. $$384 + 409$$
2. $$757 + 152$$
3. $$262 + 438$$
4. $$575 + 166$$

### Student Response

For access, consult one of our IM Certified Partners.

If students lose track of the tens or hundreds they compose (for example, $$384 + 409 = 783$$) or do not compose a ten or hundred, prompt students to explain their thinking and any representations they use. Consider asking:
• “How does your representation show that you composed a new unit?”
• “How could you use base-ten blocks to show your thinking?”

### Activity Synthesis

• Invite 2–3 previously identified students to share their representations and how they found the value of the sums.
• “How are these methods the same? How are they different?”

## Activity 2: Analyze and Add (15 minutes)

### Narrative

The purpose of this activity is for students to analyze two methods for finding a sum within 1,000. Students use what they know about adding by place and composing units to determine which method shows the correct value of the sum. Students discuss why one method did not work and ways the method could be adjusted to find the correct sum (MP3).

### Required Materials

Materials to Gather

• Groups of 2

### Activity

• “Noah and Kiran were asked to find the value of $$267 + 338$$. Take a minute to look at each student’s work.”
• 1–2 minutes: quiet think time
• “Discuss how Noah and Kiran’s work is the same and how it is different. Then explain which student found the correct value of the sum. Show how you know.”
• 10 minutes: partner work time
• Monitor for groups that match Kiran’s equations to Noah’s diagram to explain where Noah could improve his work.

### Student Facing

Noah and Kiran showed how they found the value of $$267 + 338$$.

Noah's work

Kiran's work

1. How is Noah and Kiran’s work the same? How is it different?

2. Which student found the correct value? Explain or show your thinking.

### Student Response

For access, consult one of our IM Certified Partners.

### Activity Synthesis

• “How is Noah and Kiran’s work the same? How is it different?” (They both show adding by place. Noah used a base-ten diagram and Kiran used equations. They found different values. Noah forgot to add the ten he made from the ones. He had enough tens to make a hundred.)
• “Which student found the correct value for $$267 + 338$$? How do you know?”
• Invite previously identified students to share.
• “Where do you see the step Noah missed in Kiran’s work?”

## Lesson Synthesis

### Lesson Synthesis

Display Kiran’s way and any work samples that show different methods from Activity 1.

“Today we added two three-digit numbers and looked at different methods and representations.”

“How are the methods and representations you saw today the same? How are they different?”

“Which method do you prefer? Which would you like to practice more?”

## Cool-down: Find the Sum (5 minutes)

### Cool-Down

For access, consult one of our IM Certified Partners.