# Lesson 4

More Addition and Subtraction with Tens

## Warm-up: Number Talk: Plus or Minus 10 (10 minutes)

### Narrative

The purpose of this Number Talk is to elicit strategies and understandings students have for adding and subtracting 10. These understandings help students develop fluency and will be helpful later in this lesson when students add or subtract multiples of 10.

When students share strategies based on adding or subtracting the digits in the tens place and explain why this method works, they are looking for and making use of the base-ten system and expressing regularity in repeated reasoning (MP7, MP8).

### 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.
• $$30 + 10$$
• $$40 + 10$$
• $$80 - 10$$
• $$70 - 10$$

### Student Response

For access, consult one of our IM Certified Partners.

### Activity Synthesis

• “Did anyone use the same method but would explain it differently?”
• “Did anyone approach the problem in a different way?”

## Activity 1: How Many Are in the Bag? (20 minutes)

### Narrative

The purpose of this activity is for students to solve two story problems involving adding or subtracting multiples of 10. Students are presented with a familiar context from a previous lesson in which students counted cubes in different bags. The quantities of cubes are described using representations that students are familiar with, and students add or subtract in a way that makes sense to them. The familiar context and representations are used to help students make sense of adding and subtracting tens. In the synthesis, students compare and connect the different representations used for each problem (MP2).

MLR6 Three Reads. Keep books or devices closed. To launch this activity, display only the problem stem, without revealing the question. “We are going to read this story problem three times.” After the 1st Read: “Tell your partner what happened in the story.” After the 2nd Read: “What are all the things we can count in this story?” Reveal the question. After the 3rd Read: “What are different ways we can solve this problem?”

### Required Materials

Materials to Gather

### Launch

• Groups of 2
• Give students access to connecting cubes in towers of 10 and singles and double 10-frames.

### Activity

• 7 minutes: independent work time
• 3 minutes: partner discussion
• Monitor for students who show:
• towers of 10
• base-ten drawings
• __ tens and __ tens
• expressions or equations

### Student Facing

1. Jada is counting collections of cubes.
In Bag A there are 30 cubes.
In Bag B there are 2 towers of 10.
How many cubes are in the two bags all together?
Show your thinking using drawings, numbers, or words.

2. Tyler is counting a collection of cubes.
In Bag C there are 7 towers of 10.
He takes 40 cubes out of the bag.
How many cubes does he have left in the bag?
Show your thinking using drawings, numbers, or words.

### Student Response

For access, consult one of our IM Certified Partners.

If students attempt to add or subtract using single cubes (or representations of single cubes), consider asking:

• “How are you planning to find out how many cubes there are now?”
• “How could you use what we've learned about tens to solve this problem?”

### Activity Synthesis

• Invite previously identified students to share their representations.
• “How are these representations the same? How are they different?”

## Activity 2: Add and Subtract Tens (15 minutes)

### Narrative

The purpose of this activity is for students to practice adding and subtracting multiples of 10 from multiples of 10. Students may use any method that makes sense to them, such as using connecting cubes in towers of 10, making base-ten drawings, or adding or subtracting the single-digit number of tens. When students notice they can add tens to tens just like they add single-digit numbers, they look for and make use of the base-ten structure of numbers (MP7).

Action and Expression: Develop Expression and Communication. Identify connections between the different methods students used and the way in which students showed adding or subtracting tens.
Supports accessibility for: Conceptual Processing, Organization

### Launch

• Groups of 2
• “Now you will practice adding and subtracting with tens.”

### Activity

• 5 minutes: independent work time
• 5 minutes: partner work time

### Student Facing

Equation: ____________________________

2. Subtract 20:

Equation: ____________________________

3. 4 tens and 5 tens is ___________

Equation: ____________________________

4. 8 tens take away 3 tens is __________

Equation: ____________________________

5. $$20 + 60 = \boxed{\phantom{\frac{aaai}{aaai}}}$$
6. $$70 - 20 = \boxed{\phantom{\frac{aaai}{aaai}}}$$
7. $$90 - 70 = \boxed{\phantom{\frac{aaai}{aaai}}}$$
8. $$40 + 40 = \boxed{\phantom{\frac{aaai}{aaai}}}$$

### Student Response

For access, consult one of our IM Certified Partners.

If students count on by one or do not find the numbers that make each equation true, but are able to complete the base-ten drawings and addition and subtraction statements, consider asking:

• “How did you find the number to make this equation true? How can you prove that the equation is true?”

### Activity Synthesis

• Share responses and different methods used for each problem.

## Lesson Synthesis

### Lesson Synthesis

Display $$4 + 3$$ and $$40 + 30$$.
“Today we practiced adding and subtracting tens. How are these expressions the same? How are they different?” (They are both adding 4 + 3. The first one is adding ones and the second is adding tens. You can use 4 tens + 3 tens for the second expression.)

## Cool-down: Add or Subtract Tens (5 minutes)

### Cool-Down

For access, consult one of our IM Certified Partners.

## Student Section Summary

### Student Facing

We learned how to show tens in different ways.

6 tens

60

We learned how to add and subtract tens from other tens.

$$40+10=50$$
$$50-20=30$$