# Subtraction with Perimeter & Shapes

## Objective

SWBAT use their understanding of subtraction to solve problems involving shape attributes and perimeter.

#### Big Idea

Subtraction problems can involve shapes, attributes and perimeter.

## Introduction

5 minutes

What does it mean to subtract? What do we find when we use subtraction? (The difference.)

I see a need for my students to be able to apply their understanding of subtraction to questions beyond simple subtraction questions or word problems.

Today we are going to use what we know about subtraction to help us solve other types of questions. The hardest thing with problem solving for me is figuring out which operation I need to solve, so that it what I need your help with today!

## Guided Practice

10 minutes

I need a few brave students to come teach us about these problems I have on the board.

Remember to encourage students to take risks, and be open to presenting. Developing a classroom culture that sees itself as a "support group", and a safe place to make mistakes is a critical first step. Ways to make sure everyone presents include randomizing who you call on (e.g., pulling sticks), checking in with students as they arrive (e.g., Hey, you haven't presented in awhile. I'd like to call on you today.), and by mixing it up (e.g., call on a student to call on another student, encouraging partners to present).

I use "student-led teaching" often in my classroom, especially when we are reviewing a concept. It creates a motivating context that requires students to explain their thinking and justify their answers (MP3)

## Independent Work

35 minutes

Students will create subtraction problems similar to the ones on the board on note cards today (similar to flash cards). Student will create their visual and the question on one side and their answers on the back. We will make a class set of subtraction problem cards that students will continue to work from for review.

Creating problems is like thinking of stories that we can share about ourselves and each other. Because I have modeled creating "classroom" problems from the start of the year, students are better prepared for this demanding task (creating is hard work). Of course, we are always considerate of each other's feelings when we make our "stories".

I like the way you were thinking! Now that I can see how great you are at solving these types of problems, we are going to create our own for one another to solve!

When you go back to your tables you will create subtraction problems, just like we solved on the board today, with a visual example (MP4 - Model with mathematics) and a question (MP6 - Attend to precision). Your answer goes on the back of the card, just like a flash card, so that we can have a whole set of our awesome problem solving cards!

You may do as many cards as you can, but it’s not a race. I want to see good, thoughtful and neat work so that we can use these cards for the rest of the year.

## Close

5 minutes

Great job today. Who can read me one of the cards they created? Why did you choose the words that you did? What do you think might make this card difficult for your classmates to solve?

In this video, I share an analysis of the student work product.