# Lesson 2

Add and Subtract with Tens and Hundreds

## Warm-up: Number Talk: Add Multiples of 10 (10 minutes)

### Narrative

The purpose of this Number Talk is to elicit strategies and understandings students have for adding multiples of 10 to two- and three-digit numbers. This activity helps students extend their fluency with adding multiples of 10 to two-digit numbers to their work in the lesson activities with adding and subtracting multiples of 10 and 100 within 1,000. As students share their thinking, consider recording on an open number line.

### 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

• Record answers and strategy on an open number line.
• Keep expressions and work displayed.
• Repeat with each expression.

### Student Facing

Find the value of each expression mentally.

• $$34 + 20$$
• $$34 + 60$$
• $$58 + 30$$
• $$158 + 40$$

### Student Response

For access, consult one of our IM Certified Partners.

### Activity Synthesis

• “How did you find the value of these expressions?” (We noticed we could count on by tens. We added the number of tens in each one. The number in the ones place didn’t change.)

## Activity 1: Show It with Base-ten Blocks (15 minutes)

### Narrative

The purpose of this activity is to add and subtract three-digit numbers and multiples of 10 or 100 using base-ten blocks and equations. The structure of the base-ten blocks encourages students to notice that hundreds are added to or subtracted from hundreds and tens are added to or subtracted from tens (MP7). To help students focus on this structure, the numbers are chosen so that the addition and subtraction of tens can take place without needing to compose or decompose a hundred.

If you do not have enough hundred blocks for each group of 2 students, students may work in larger groups.

### Required Materials

Materials to Gather

### Launch

• Groups of 2
• Give each group base-ten blocks and a number cube.

### Activity

• “Work with your partner to show each number with base-ten blocks.”
• “Take turns rolling the number cube to see how many tens or hundreds to add or subtract.”
• 10 minutes: partner work time
• Monitor for students to share their equations for the number of hundreds they subtract from 805.

### Student Facing

Use your base-ten blocks to show each number. Then, roll a number cube to see how many tens or hundreds to add or subtract.

1. Show 297.

2. Complete the equation: $$297 + \underline{\hspace{1cm}} =\underline{\hspace{1cm}}$$
2. Show 432.

2. $$432 + \underline{\hspace{1cm}} =\underline{\hspace{1cm}}$$
3. Show 982.

1. Subtract _____ tens.
2. $$982 - \underline{\hspace{1cm}} =\underline{\hspace{1cm}}$$
4. Show 351.

2. Write an equation:
5. Show 805.

1. Subtract ____ hundreds.
2. Write an equation:

### Student Response

For access, consult one of our IM Certified Partners.

### Activity Synthesis

• Invite previously identified students to share equations or display
• $$805 - 400 = 405$$
• Display a base-ten diagram, or, if possible, allow students to demonstrate with base-ten blocks.
• “How does the equation connect to the diagram or blocks?” (You take away 4 hundreds from the blocks and you’re left with 4 hundreds and 5 ones.)
• “What did you notice about how the value of the blocks changed?” (There are fewer blocks. The hundreds place changed because you subtracted hundreds.)

## Activity 2: How Many with Base-ten Blocks and Equations (20 minutes)

### Narrative

The purpose of this activity is for students to add and subtract multiples of 10 and 100 within 1,000. Students interpret situations with base-ten blocks and base-ten diagrams and use equations to represents sums and differences. In the activity synthesis, students relate the situation, base-ten diagram, and equation and notice, through repeated reasoning, that when adding and subtracting, one can add or subtract hundreds and hundreds and tens and tens (MP7, MP8).

MLR7 Compare and Connect. Synthesis: Lead a discussion comparing, contrasting, and connecting their different ways of representing the value of Mai and Lin’s blocks together. Ask, “How do these different representations show the same information?” “How are they different?”
Representation: Access for Perception. Invite students to act out the scenario of giving and taking hundreds on a number line. Discuss the individual jumps of 100 if a jump of 400 is too much to begin.
Supports accessibility for: Conceptual Processing, Language, Organization

### Required Materials

Materials to Gather

• Groups of 2

### Activity

• “These students were using base-ten blocks to find the value of sums and differences.”
• “For each problem, represent the student’s value in a way that makes sense to you. You can use base-ten blocks, diagrams, or equations.”
• 10 minutes: partner work time
• For Priya and Jada’s blocks, monitor for students who:
• write equations to show the sums and differences.
• use base-ten diagrams to show subtraction.

### Student Facing

1. Mai has 2 hundreds, 2 tens, and 3 ones. Lin has 4 hundreds.

Represent their values with base-ten blocks or diagrams.

What is the value of their blocks altogether? Show your thinking.

2. Andre has 4 hundreds, 2 tens, and 8 ones.

Represent his value with base-ten blocks or diagrams.

Andre gives 2 hundreds to Clare.

What is the value of his blocks now? Show your thinking.

3. Diego has 6 tens. Tyler has 8 hundreds, 3 tens, and 6 ones.

What is the value of their blocks together? Show your thinking.

4. Elena has 5 hundreds, 7 tens, and 2 ones. She gives 2 tens to Kiran.

What is the value of her blocks now? Show your thinking.

5. Priya has 6 hundreds, 5 tens, and 8 ones. Han gives her 3 hundreds.

What is the value of her blocks now? Show your thinking.

6. Jada has 4 hundreds, 8 tens, and 2 ones. She gives 3 hundreds to Noah.

What is the value of her blocks now? Show your thinking.

### Student Response

For access, consult one of our IM Certified Partners.

If students draw diagrams that do not match the situation or write equations that are not true, consider asking:

• “Can you explain what you did?”
• “Do you notice any patterns when you add or subtract hundreds and hundreds? Tens and tens?”

### Activity Synthesis

• Invite a student to share their representation and equation for Jada’s blocks. If no students use a base-ten diagram, select a student to share how they use base-ten blocks, and use a base-ten diagram to record their steps.
• “How does the base-ten diagram show Jada’s blocks?” (The blocks show how many Jada started with. The lines show the 3 hundreds that were taken away.)
• Display $$482 - 300 = 182$$
• “How does the equation show Jada’s blocks?” (482 is what Jada started with and 300 is the 3 hundreds she gave away. 182 is how much she has left.)

## Lesson Synthesis

### Lesson Synthesis

“Today you added and subtracted hundreds or tens to and from three-digit numbers.”

Invite previously identified students to share representations for Priya’s blocks.

Display $$658 + 300 = 958$$.

“How is the representation of Jada’s blocks different from the representation for Priya’s blocks?” (Jada’s blocks show 3 hundreds crossed out. Priya’s show 3 hundreds added.)

## Cool-down: How Many Blocks? (5 minutes)

### Cool-Down

For access, consult one of our IM Certified Partners.