# Lesson 12

Subtract From a Teen Number

## Warm-up: Choral Count: By Ten (10 minutes)

### Narrative

The purpose of this Choral Count is to invite students to practice counting on by 10 and notice patterns in the count. These understandings help students develop fluency and will be helpful when students make use of the base-ten structure (MP7).

### Launch

• “Count by 10, starting at 2.”
• Record as students count.
• Stop counting and recording at 52.

### Activity

• “What patterns do you see?”
• 1–2 minutes: quiet think time
• Record responses.

### Student Response

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### Activity Synthesis

• “Who can restate the pattern in different words?”
• “What do you predict would come after 82? Why?”

## Activity 1: Noah’s Collection (15 minutes)

### Narrative

The purpose of this activity is for students to solve a Take From, Result Unknown story problem in which the minuend is in the teens. Students solve using any method that makes sense to them, which could include using double 10-frames, connecting cubes, or drawings, and counting back or counting on (MP1).

Monitor and select students with the following methods to share in the synthesis:

• cross off 8 and count remaining or see it as 10 and 1
• count on from 8 to 19
• know the ten stays the same, subtract $$9 - 8$$
Representation: Internalize Comprehension. Synthesis: Record students’ strategies on a display and keep it visible during the next activity.
Supports accessibility for: Conceptual Processing, Organization

### Required Materials

Materials to Gather

### Launch

• Groups of 2
• Give students access to double 10-frames and connecting cubes or two-color counters.

### Activity

• 4 minutes: independent work time
• 3 minutes: partner discussion
• Monitor for students using methods listed in the narrative.

### Student Facing

Noah likes to collect game pieces.
He has 19 game pieces arranged like this in his bin.

He takes out 8 game pieces to play with.
How many game pieces are left in the bin?
Show your thinking using drawings, numbers, or words.

Equation: ________________________________

### Student Response

For access, consult one of our IM Certified Partners.

### Activity Synthesis

• “What do you notice about how the game pieces are organized? How can that help us solve the story problem?” (They are in two 10-frames. Since I know there are 5 in each row, I can take away 5 and then 3 more.)
• Invite previously identified students to share in the given order.
• “How are these methods the same? How are they different?” (They are the same because they all show 19 game pieces and the 8 he took out. They all got 11. They are different because one counts on, one counts back, and the other doesn't count at all.)
• “What equation could we write to represent the problem?” ($$19 - 8 = \boxed{11}$$, $$8 + \boxed {11} = 19$$)

## Activity 2: Addition and Subtraction Equations with Teen Numbers (10 minutes)

### Narrative

The purpose of this activity is for students to find the value that makes the addition and subtraction equations true using methods that make sense to them. Each equation has a total within 20 and one part that is a teen number.

### Required Materials

Materials to Gather

### Launch

• Groups of 2
• Give students access to double 10-frames and connecting cubes or two-colors counters.

### Activity

• “You will work on your own at first, then you will share with a partner.”
• 5 minutes: independent work time
• 3 minutes: partner discussion
• Monitor for students who find the value that makes the equation $$19 - 8 = \boxed{\phantom{3}}$$ true by taking away 8 or counting on from 8 to 19 using double 10-frames and counters or drawings. These methods will be discussed in the lesson synthesis.

### Student Facing

Find the number that makes each equation true.

Be ready to explain your thinking in a way that others will understand.

1. $$13 + 4 = \boxed{\phantom{\frac{aaai}{aaai}}}$$
2. $$16 + \boxed{\phantom{\frac{aaai}{aaai}}} = 17$$
3. $$19 - 8 = \boxed{\phantom{\frac{aaai}{aaai}}}$$
4. $$14 - 2 = \boxed{\phantom{\frac{aaai}{aaai}}}$$
5. $$11 + \boxed{\phantom{\frac{aaai}{aaai}}} = 17$$
6. $$\boxed{\phantom{\frac{aaai}{aaai}}} + 1 = 18$$

### Student Response

For access, consult one of our IM Certified Partners.

### Activity Synthesis

• Display each equation with the missing value.

## Activity 3: Introduce Shake and Spill, Cover (up to 20) (15 minutes)

### Narrative

The purpose of this activity is for students to learn stage 5 of the Shake and Spill center. Students use between 11-20 counters. One partner shakes, spills, and covers up the yellow counters with a cup. The other partner determines how many counters are under the cup and explains how they know. Both partners record the round with an equation.

MLR8 Discussion Supports. Synthesis: Provide students with the opportunity to rehearse what they will say with a partner before they share with the whole class.

### Required Materials

Materials to Gather

Materials to Copy

• Shake and Spill Stage 4 and 5 Recording Sheet (G1 and 2)

### Launch

• Groups of 2
• Give each group a cup, two-color counters, and recording sheets.
• “We are going to learn a new way to play the Shake and Spill center. We will play Shake and Spill, Cover, with more than 10 counters.”
• “First, you and your partner decide how many counters you want to use. You can use 11–20 counters. Then you play the same way we have played in the past. One partner shakes and spills the counters and covers the yellow counters with the cup. Their partner needs to figure out how many yellow counters are under the cup. Then both partners write an equation to match the counters.”

### Activity

• 10 minutes: partner work time

### Activity Synthesis

• Display five red counters and cover ten yellow counters under the cup.
• “My partner and I are playing with 15 counters. How many yellow counters are under the cup? How do you know?”

## Lesson Synthesis

### Lesson Synthesis

“Today we added and subtracted with teen numbers.”

Display $$19 - 8 = \boxed{\phantom{3}}$$.

Invite previously identified students to share.

“Which method would you recommend to a friend? Why?” (I would recommend building numbers on 10-frames and taking away because it’s easier to use the counters. I would recommend counting on because it is faster than using counters.)

## Cool-down: Unit 3, Section B Checkpoint (0 minutes)

### Cool-Down

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