## Explaining Their Thinking - Section 1: Warm Ups

# NO FLIPPING SUBTRACTION

Lesson 14 of 15

## Objective: SWBAT subtract 2-digit numbers using pictures, while remembering that numbers cannot be flipped.

*35 minutes*

#### Warm Ups

*10 min*

Yesterday I introduced the idea of NO FLIPPING subtraction. Today I start the warm up with a review of the NO FLIPPING poster and ask students what it means. I have volunteers explain why the poster is up (if the don't have enough ones, we can't just switch the numbers to subtract from the greater number of ones).

Now I put a problem on the board vertically. It is 35 - 19. I ask students how I might solve the problem? I ask for 2 volunteers to come up and show us their solution, once they have written/drawn/counted their solutions. I ask the class if they followed the No Flip Rule? We check to make sure that they didn't flip the numbers as they solved the problems.

I ask all students to solve another problem that I put on the board. I write vertically 72 - 43. I give students time to work out a solution and then we share 2 solutions. I always tell students that I know there are more solutions, but today we are only going to share a few.

I give each student a NO FLIPPING mini-poster to put in their math suitcase.

When I feel that most of the students are understanding what we are doing, I tell them that at the beginning of math today they will be trying to solve some word problems. I tell them that I will give them the problems and a separate sheet to use if they need it, to solve the problems. I tell them to use the tools in their suitcases to help them solve the problems.

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#### Word Problems

*25 min*

I hand out a practice page word problems.docx. I want students to model with math (MP4), as they work to persevere in solving the problems. (MP1). I invite the children who were struggling in the warms up to bring their papers to the table where we can work together. I encourage students to draw the blocks, or to take out the actual blocks to solve the problems given.

The problems are subtraction word problems. I have put the subtraction houses on the first 3 problems. I hope that the students will put the houses on the last 3 problems on their own. I want to see how they model with mathematics for this problems (MP4).

I have students who are finished quickly work on IPAD math fact practices.

#### Resources

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- UNIT 1: What and Where is Math?
- UNIT 2: Adding and Subtracting the Basics
- UNIT 3: Sensible Numbers
- UNIT 4: Sensible Numbers
- UNIT 5: Everything In Its Place
- UNIT 6: Everything in Its Place
- UNIT 7: Place Value
- UNIT 8: Numbers Have Patterns
- UNIT 9: Fractions
- UNIT 10: Money
- UNIT 11: The Numbers Are Getting Bigger
- UNIT 12: More Complex Numbers and Operations
- UNIT 13: Area, Perimeter and More Measurement
- UNIT 14: Length
- UNIT 15: Geometry
- UNIT 16: Getting Ready to Multiply
- UNIT 17: Getting Better at Addition and Subtraction
- UNIT 18: Strategies That Work

- LESSON 1: Adding Three or More Numbers
- LESSON 2: Houses of Addition
- LESSON 3: Comparing the Weather
- LESSON 4: Balancing and Comparing Data
- LESSON 5: Subtraction Houses
- LESSON 6: Subtraction Houses Part 2
- LESSON 7: Time to Practice
- LESSON 8: A Suitcase of Math Strategies
- LESSON 9: What Do I Need?
- LESSON 10: SMALL, SMALL, BIG
- LESSON 11: Keeping It In The Field
- LESSON 12: Going For The Gold
- LESSON 13: Checking on Subtraction
- LESSON 14: NO FLIPPING SUBTRACTION
- LESSON 15: Assessment