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# Stop, Look and Check

Lesson 8 of 16

## Objective: SWBAT determine if it is necessary to regroup to complete a subtraction problem.

#### Warm Up

*10 min*

I write two problems, each written vertically, on the board:

82 - 56 = 34

82 - 56 = 26

I ask students to take out their math journals and check the 2 problems. I tell them to decide which one is correct and which one is not and why. This is asking students to construct a viable argument and critique the ideas of others (MP3).

I am looking to see if students will just flip the 2 and 6 in the first problem to solve 6 - 2 = 4 in the ones place and 80 - 50 = 30 for the tens place.

I give students a few minutes to solve the problems and then I ask them to close their eyes and vote on which one is correct. After we vote I ask for volunteers to explain why they thought one or the other were correct.

We discuss the ways students figured out the problem.

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#### STOP, LOOK and CHECK

*15 min*

Today I hand each student a small stop sign with eyes and a check mark on it.stop look check.docx I tell them that when I subtract I first need to go to the ones column (written vertically) and **stop** (I draw a stop sign around the number of ones to be subtracted), use my eyes to **look**, and **check** (I draw a check mark on the bigger number of ones.) If the check mark is on the top, I can subtract because the bigger number is on top. If the check mark is on the bottom, I have to borrow because the bigger number is on the bottom.

I hand each student a paper with 4 double-digit subtraction problems on it. I ask them to **stop**, and draw the stop sign around each lower number, **look **at both digits in the ones place and **check** the biggest one. I am trying to teach students to attend to the structure of the problem (MP 7) as they learn more about regrouping.

Now if the check mark is on the top they can subtract, but if it is on the bottom, they will need to borrow a ten first. I point out that bottom and borrow both begin with B to help us remember which is which.

After I see that everyone has stopped, looked and checked all 4 problems, I ask them which of the problems they will need to borrow on. Then I remind them of the base ten or tens frame drawings that they can use to solve the problems.

I give them time to solve the problems and then we share what we did.

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#### Independent Practice

*15 min*

I write a series of double-digit subtraction problems on the board. I ask students to copy them onto a blank piece of paper and then use the **stop**, **look** and **check** process to decide whether they need to borrow or not.

I tell students they can then use their favorite strategies to complete the problems.

I give students time to complete the problems on their own. I circulate around the room to listen to student thinking and to help struggling students.

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#### Closing

*15 min*

I ask students to pair up with the person across from them and to share their solutions to the problems. I ask them to look and see if they needed to borrow, and then to share answers. If they did not agree, they should talk about how the problem could be done, and then use another method to find an answer together.

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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: My Special Strategies
- LESSON 2: Division Strategies
- LESSON 3: Estimation as a Strategy for Checking Work
- LESSON 4: Using Math at Work
- LESSON 5: Measurement Strategies
- LESSON 6: Double-Digit Subtraction - We Can Do It
- LESSON 7: Where On The Line?
- LESSON 8: Stop, Look and Check
- LESSON 9: Stop, Look and Check (Part 2)
- LESSON 10: Attributes of Groups
- LESSON 11: Relative Size
- LESSON 12: Counting Coins Again
- LESSON 13: Another Visit to Double-Digit Work
- LESSON 14: Visiting the Olympics
- LESSON 15: Creating Math Games
- LESSON 16: Playing Our Own Games