## HOW MANY COOKIES? HOW MANY CRACKERS? [DAY 4]

### ADDING AND SUBTRACTING WITHIN 100

Introduction to using place value strategies to add and subtract within 100

#### Intentionality

#### Math Talk

#### Purposeful Practice

#### Resources & Downloads

#### Educator Discussion Area

## Intentionality & Unit Overview

### Length of Unit: 6 Days

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Students will explore the place value strategy of subtracting in parts starting from a non-multiple of ten minuend (the number being subtracted from, for example in the equation 5 – 2 = 3, 5 is the minuend).

## 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 independent purposeful practice. The math talk and purposeful practice serve to develop a deeper understanding of the following big ideas.

- The action of removal is represented by subtraction.
- Application of knowledge of decomposition within 10 to solve problems involving addition and subtraction of two digit numbers.
- Addition and subtraction problems within 100 can be solved using strategies along a developmental continuum of counting all, counting on/back, and using place value strategies.
- When students are using place value strategies to solve addition and subtraction problems within 100, they are using their understanding of tens and ones and decomposition to accurately, flexibly, and efficiently solve problems. See the Student Approaches section in this guide for examples.

Note:

Minuend: The quantity from which another quantity, the subtrahend, is to be subtracted. In the equation 50 − 16 = 34, the minuend is 50.

Subtrahend (the number to be taken from another (which is called the *minuend*) in the operation of subtraction.

Definitions from Wordnik

## Math Talk

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## Purposeful Practice

## While Students Are Practicing…

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## Questions: Subtracting Within 100

### Question #1:

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### Question #2:

### Question #3:

### Question #4:

**Consider Revisiting Closest to Zero**

Closest to Zero is a game that practices subtracting using a place value strategy.

While your students play or during a wrap discussion, the central point to talk about is how when we are subtracting 26, we can do that by first subtracting 2 tens and then subtracting 6 ones. Some students may subtract the ones before the tens which is also fine.

Another interesting point to discuss is how students handle a situation such as 72 – 18 or 64 – 19, where the subtrahend has more ones than the minuend. So they break up the ones to stop at a multiple of ten? Do they subtract all of the ones at once?

We suggest collecting this reflection as an additional opportunity to engage in the formative assessment process to inform next steps for individual students as well as how the whole class will proceed.

## Resources & Downloads

#### Printable Lesson Plan PDF

#### Videos, Images & Media Files

#### Apple Keynote Presentation

#### Powerpoint Presentation

#### Printable Consolidation Prompts

## Educator Discussion Area

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