## SCHOOL OF FISH [DAY 4]

### DEVELOPING PLACE VALUE UNDERSTANDING

Explore efficient strategies to subtract values within 50

#### Intentionality

#### Math Talk

#### Visual Math Talk Prompt #1

#### Visual Math Talk Prompt #2

#### Visual Math Talk Prompt #3

#### Visual Math Talk Prompt #4

#### Visual Math Talk Prompt #5

#### Purposeful Practice

#### Resources & Downloads

#### Educator Discussion Area

## Intentionality & Unit Overview

### Length of Unit: 5 Days

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Students will deepen their understanding of subtracting 10, on and off a decade number. As well as subtracting single digits from a decade number.

**Intentionality…**

The purpose of the Day 4 activities is to reinforce key concepts from Day 3. Students will engage in a string of related problems through a math talk and will have an opportunity to complete purposeful practice. The math talk and purposeful practice serve to develop a deeper understanding of the following big ideas.

Some of the big ideas that may emerge through this task include:

- Understanding hierarchical inclusion allows for flexible composing and decomposing of numbers
- Numbers can be decomposed by separating a whole into two or more parts
- Subtraction names the missing part in terms of the whole
- Different subtraction situations will elicit different strategies
- Number relationships provide the foundation for strategies to help students remember basic facts
- Subtraction can be used in either take away, comparison, or missing addend situations. This task will explore the take away method.
- Models can be used to connect concrete to abstract

Before starting this unit, students should be familiar with:

- Facts of 10 ( e.g., 6+4 = 10, 10-4 = 6)
- Flexibility when decomposing numbers (e.g., 13 can be decomposed into 10 and 3, but also 9 and 4, 8 and 5, etc)

The Down and Under Ten strategy which can be explored in the Fruit Picking Unit.

## Math Talk

To practice adding on and off the decade number, have your students work through these problems one at a time. As you present each problem, provide students with some quiet, individual think time during which they can solve the problem and show their thinking on a dry erase board, paper, etc. Then have students share their thinking either in pairs or with the whole group. As you facilitate these conversations, emphasize that 10 can be subtracted from a number by using place value understanding. We can subtract 10 without having to count back because it is removing a group of 10 from the “tens place value”.

The problems are supporting the move towards subtracting numbers mentally and creating number sense. Students should be encouraged to do parts of the subtracting in their head, and removing the tens is a foundational step as students are introduced to more difficult problems. Manipulatives may be necessary for students to “see” how there is a unit of 10 being removed. For this purpose, base ten blocks are used in the visual prompt as well as an open number line.

String of Prompts:

*String 1:*

*String 1:*

*20 – 10*

*20 – 10*

*30 – 10*

*30 – 10*

*50 – 10*

*50 – 10*

*String 2:*

*String 2:*

*18 – 10*

*18 – 10*

*27 – 10*

*27 – 10*

*45 – 10*

*45 – 10*

*String 3:*

*String 3:*

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*String 4:*

*String 4:*

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*String 5:*

*String 5:*

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## Visual Math Talk Prompt #1

**Facilitator Note:** The base ten blocks are used in these prompts as a visual to demonstrate that a unit of ten has been removed. The action of removal may need to be demonstrated in “real time” to assist some students. Consider providing base ten blocks to some students or demonstrate as a group.

Students will identify how many blocks they see. It is important to establish that these are base ten rods, as they may look different than the ones used in your classroom.

As the prompt continues, students will watch as 10 is removed from 20. We want students to see that when a base ten rod (10) is removed, 1 is taken from the tens place value. This idea will be used throughout the rest of the prompts.

With 30 – 10, take time to establish that again we are removing a base ten rod (10) from 30 so we need to adjust the tens place value by one. We want to encourage/solidify that this process can be done mentally.

## Visual Math Talk Prompt #2

In this second string, we are still removing a base ten rod (10) but this time it is “off the decade”. This process should still be the same as removing 10 from a decade number but take time to solidify it for students. We want students to be comfortable subtracting 10 on and off a decade number.

On the decade: 20 – 10 or 40 – 10

Off the decade: 18 – 10 or 37 – 10

## Visual Math Talk Prompt #3

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## Visual Math Talk Prompt #4

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## Visual Math Talk Prompt #5

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## Purposeful Practice

## Small Group Game

## Small Group Assessment Opportunity

## Resources & Downloads

## Educator Discussion Area

## Explore Our 60+ Problem Based Units

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