# Lesson 11

## Warm-up: True or False: Tens and Ones (10 minutes)

### Narrative

The purpose of this True or False is to elicit insights students have about adding two-digit numbers using place value understanding. This will be helpful later when students add a two-digit number and a multiple of 10.

### Launch

• Display one statement.
• “Give me a signal when you know whether the statement is true and can explain how you know.”
• 1 minute: quiet think time
Activity
• Share and record answers and strategy.
• Repeat with each equation.

### Student Facing

Decide if each statement is true or false.
Be prepared to explain your reasoning.

• $$80 + 5 = 5 + 80$$

• $$70 + 1 = 80 + 1$$

• $$20 + 6 = 6 + 30$$

### Student Response

For access, consult one of our IM Certified Partners.

### Activity Synthesis

• “How can you use what you know about tens and ones to reason about the equations?” (Two numbers are not equal if the number of ones is the same but the tens is different.)

## Activity 1: Add Two-digit Numbers and Tens (20 minutes)

### Narrative

The purpose of this activity is for students to add multiples of 10 and two-digit numbers in a way that makes sense to them. Students may use connecting cubes in towers of 10 and singles. They represent their thinking using drawings, numbers, or words. Some students may make base-ten drawings to show the addition, while others may find the sum mentally, applying what they have learned about place value in previous lessons. Some students may use both methods, depending on the numbers in the problem.

### Launch

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

### Activity

• 10 minutes: partner work time
• Monitor for students who find the sum of 30 + 65 by:
• drawing and counting by ten, then one
• count on from 65 by ten: 75, 85, 95
• combine 3 tens and 6 tens, then add 5 ones

### Student Facing

Find the number that makes each equation true.
Show your thinking using drawings, numbers, or words.
1. $$37 + 20 = \boxed{\phantom{\frac{aaai}{aaai}}}$$

2. $$60 + 23 = \boxed{\phantom{\frac{aaai}{aaai}}}$$

3. $$48 + 50 = \boxed{\phantom{\frac{aaai}{aaai}}}$$

4. $$\boxed{\phantom{\frac{aaai}{aaai}}} = 54 + 20$$

5. $$30 + 65 = \boxed{\phantom{\frac{aaai}{aaai}}}$$

### Student Response

For access, consult one of our IM Certified Partners.

### Activity Synthesis

• Invite previously identified students to share.
• “How are these methods the same? How are they different?” (They all added tens to tens. Some people started with the first number and other people started with the second number.)

## Activity 2: The Missing Digit (15 minutes)

### Narrative

The purpose of this activity is for students to use their understanding of place value to make an equation true when a digit in a two-digit number is “missing.” Students consider the values of the digits in order to justify their thinking. Students may use connecting cubes in towers of 10 and singles, create drawings, or write about their reasoning.

MLR8 Discussion Supports. Prior to solving the problems, invite students to make sense of the situations and take turns sharing their understanding with their partner. Listen for and clarify any questions about the context.
Action and Expression: Internalize Executive Functions. Invite students to decide with their partners what tools they will use to find the missing digit. Allow time for students to organize tools.
Supports accessibility for: Organization, Attention

### Launch

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

### Activity

• 10 minutes: partner work time

### Student Facing

1. This equation is true.

What digit is under the smudge?
Show your thinking using drawings, numbers, or words.

2. This equation is not true.

### Student Response

For access, consult one of our IM Certified Partners.

### Activity Synthesis

• Invite students to share how they determined the missing digit in the first equation.
• Invite students to share how they know the second equation cannot be true.

## Lesson Synthesis

### Lesson Synthesis

Display $$34 + 40$$.

“Today we added tens to two-digit numbers. What do we know about adding these numbers?” (It’s like counting on by tens. You can think of it as 34 and 4 more tens. You can just add the number of tens in each number. For example, 3 tens + 4 tens is 7 tens.)

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

### Cool-Down

For access, consult one of our IM Certified Partners.

## Student Section Summary

### Student Facing

We learned that two-digit numbers are made up of tens and ones.

We represented two-digit numbers in many different ways.

$$60+5$$
$$42 + 50 = \boxed{92}$$