# Lesson 1

## Warm-up: How Many Do You See: 10-frames (10 minutes)

### Narrative

The purpose of this How Many Do You See is for students to subitize or use grouping strategies to describe the images they see. When students look for ways to see and describe numbers as groups of tens and ones and connect this to two-digit numbers, they look for and make use of the base-ten structure (MP7).

### Launch

• Groups of 2
• “How many do you see? How do you see them?”
• Flash image.
• 30 seconds: quiet think time

### Activity

• Display image.
• 1 minute: partner discussion
• Record responses.
• Repeat for each image.

### Student Facing

How many do you see?
How do you see them?

### Activity Synthesis

• “How did we describe the second image using tens and ones? How many tens do you see? How many ones?” (Some people said they saw it as 3 tens and 5 ones.)
• “How could we describe the last image using tens and ones?” (3 tens and 9 ones)
• “How could we write equations to go with the last image?” ($$35 + 4 = 39$$ or $$30 + 9 = 39$$)

## Activity 1: What Did I Add? (20 minutes)

### Narrative

The purpose of this activity is for students to apply their place value understanding to add an amount of tens or ones to a two-digit number. Students also use place value reasoning to determine whether a number of tens or ones was added to a two-digit number. Throughout the activity, students explain how they add and how they determined the unknown addend with an emphasis on place value vocabulary (MP3, MP6).

MLR2 Collect and Display. Circulate, listen for and collect the language students use as they talk with their partners. On a visible display, record words and phrases such as: tens, ones, sum, equation, starting number, secret number. Invite students to borrow language from the display as needed, and update it throughout the lesson.
Representation: Internalize Comprehension. Synthesis: Invite students to identify which details were most important to solve the problem. Display the sentence frame, “The next time I add a two-digit and one-digit number, I will pay attention to . . . .“
Supports accessibility for: Conceptual Processing, Organization

### Required Materials

Materials to Gather

### Launch

• Groups of 2
• Give each group a set of number cards and a paper clip. Give students access to connecting cubes in towers of 10 and singles.
• “Remove the 0, 6, 7, 8, 9 and 10 from the number cards.”
• “We are going to play a game where you must figure out the number your partner added. Let’s play a round together. All of you are partner A and I am partner B.”
• Invite a student to spin.
• “You spun (43). I will draw a number card and decide whether to add that many ones or that many tens. I will say the sum aloud.”
• “The sum is (93). What number did I add? Talk with your partner. Be ready to explain how you know.” (You added 50. In order to get from 43 to 93 you add 5 tens. 53, 63, 73, 83, 93.)
• 1 minute: partner discussion
• Share responses.

### Activity

• “Now you will play with your partner. For each round, decide whether you will add tens or ones and see if your partner can guess what you added.”
• 15 minutes: partner work time
• As students work, consider asking:
• “How did you choose to add tens or ones?”

### Student Facing

• Partner A: Spin to get a starting number.

• Partner B: Pick a number card without showing your partner. Choose whether to add that many ones or tens to your starting number. Make sure you don't go over 100. Tell your partner the sum.
• Switch roles and repeat.

### Activity Synthesis

• “Priya’s partner landed on 34 on the spinner. Priya picked a 5. If she wants to add 5 ones, how could she find the sum?“ (She could count on. 35, 36, 37, 38, 39. She could add 5 more ones to the 4 ones in 34. 4 + 5 = 9 so its 39.)
• “How can she find the sum if she wants to add 5 tens?“ (She could count on by tens. 44, 54, 64, 74, 84. She could add 3 tens and 5 tens and get 8 tens.)

## Activity 2: Add Tens or Ones (15 minutes)

### Narrative

In this activity, students add a one-digit number or a multiple of 10 and a two-digit number, without composing a ten. The order of the problems encourages students to analyze the difference between adding ones or tens (adding 5 or adding 50), which builds on the previous activity. Students rely on methods that they have learned such as counting on or using known facts to add. In the synthesis, students may say they notice that only the digit in the ones place of a two-digit number changes when they add a one-digit number to it. While this statement is true about the numbers in these problems, it will not be true when students add in future work. It may be helpful to record this conjecture on chart paper and revisit it again in future lessons to allow students an opportunity to explain whether or not it is always true.

### Launch

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

### Activity

• 7 minutes: independent work time
• 3 minutes: partner discussion

### Student Facing

Find the number that makes each equation true.

1. $$43 + 5 = \boxed{\phantom{\frac{aaai}{aaai}}}$$
2. $$43 + 50 = \boxed{\phantom{\frac{aaai}{aaai}}}$$
1. $$51 + 3 = \boxed{\phantom{\frac{aaai}{aaai}}}$$
2. $$51 + 30 = \boxed{\phantom{\frac{aaai}{aaai}}}$$
1. $$2 + 75= \boxed{\phantom{\frac{aaai}{aaai}}}$$
2. $$20 + 75 = \boxed{\phantom{\frac{aaai}{aaai}}}$$
1. $$93 + 6 = \boxed{\phantom{\frac{aaai}{aaai}}}$$

Show your thinking using drawings, numbers, or words.

2. $$60 +28 = \boxed{\phantom{\frac{aaai}{aaai}}}$$

Show your thinking using drawings, numbers, or words.

3. $$5 + 74 = \boxed{\phantom{\frac{aaai}{aaai}}}$$

Show your thinking using drawings, numbers, or words.

### Student Response

If students fill in both equations with the same number, consider asking:

• “How did you find the number that makes each equation true?”
• “How would each expression look with connecting cubes? Would there be the same number of cubes?”

### Activity Synthesis

• Display the first three problems.
• “What did you notice about the equations and the sums?” (It was like adding the same number, just to a different place. When I add $$43 + 5$$, I only added the numbers in the ones place. When I add $$43 + 50$$, I added 5 tens and 0 ones to 43. The number in the ones place stayed the same.)

## Lesson Synthesis

### Lesson Synthesis

“Today we added tens or ones to two-digit numbers. Mai and Andre added 4 + 45. Mai says the sum is 85. Andre says the sum is 49. Who do you agree with? Why do you agree with them?”(Mai added the 4 to the 4 tens in 45 to get 85. Andre added the 4 to the 5 ones in 45 to get 49. I agree with Andre, because 4 means 4 ones so you have to add the 4 to the ones. Mai added 4 tens which is 40.)