## Objective

Use constant difference to subtract by subtracting multiples of ten or a hundred.

### Student-Facing

I can make a friendly number to subtract multiples of ten or hundred.

## Common Core Standards

### Core Standards

The core standards covered in this lesson

2.NBT.B.7— Add and subtract within 1000, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method. Understand that in adding or subtracting three-digit numbers, one adds or subtracts hundreds and hundreds, tens and tens, ones and ones; and sometimes it is necessary to compose or decompose tens or hundreds.

### Number and Operations in Base Ten

2.NBT.B.7— Add and subtract within 1000, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method. Understand that in adding or subtracting three-digit numbers, one adds or subtracts hundreds and hundreds, tens and tens, ones and ones; and sometimes it is necessary to compose or decompose tens or hundreds.

### Foundational Standards

The foundational standards covered in this lesson

1.NBT.B.2

### Number and Operations in Base Ten

1.NBT.B.2— Understand that the two digits of a two-digit number represent amounts of tens and ones. Understand the following as special cases:

2.NBT.A.1

### Number and Operations in Base Ten

2.NBT.A.1— Understand that the three digits of a three-digit number represent amounts of hundreds, tens, and ones; e.g., 706 equals 7 hundreds, 0 tens, and 6 ones. Understand the following as special cases:

2.NBT.A.2

### Number and Operations in Base Ten

2.NBT.A.2— Count within 1000; skip-count by 5s, 10s, and 100s.

## Criteria for Success

The essential concepts students need to demonstrate or understand to achieve the lesson objective

- Recognize how and compose a multiple of 10 or 100 with the subtrahend by adding.
- Add the same amount to the minuend to keep the difference in the problem and convert to an easier problem.
- Use a mental strategy to complete the subtraction by subtracting a multiple of 10 or 100.

## Tips for Teachers

Suggestions for teachers to help them teach this lesson

Using tape diagrams to represent the minuend and subtrahend can be a helpful way for students to visualize why constant-difference works as a subtraction strategy. Students see that when the same amount is added to both numbers, the difference is preserved. Unit 2 Lesson 12 explores the idea of constant difference within 100 if students need a refresher before applying to computations within 1,000.

## Warm Up

5-10 minutes

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## Anchor Tasks

Tasks designed to teach criteria for success of the lesson, and guidance to help draw out student understanding

15-25 minutes

### Problem 1

a.How much more to the next multiple of 10? What is it?

- 48
- 77
- 95

b.How much more to the next multiple of 100? What is it?

- 98
- 190
- 394

#### Purpose

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#### Facilitation Guidance

Unlock Facilitation Guidance to make the most of each Anchor Task. Find tips to launch tasks, support all students, and synthesize new learning. Download a sample.

### Problem 2

Karla solved 310 - 99 = ? by making a friendly number to subtract.

a.What do you notice about Karla's strategy?

b.Use Karla's strategy and make the next multiple of ten or a hundred to subtract.

- 400 - 97 = _____
- 525 - 295 = _____
- 400 - 198 = _____
- 446 - 39 = _____

#### Purpose

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#### Facilitation Guidance

Unlock Facilitation Guidance to make the most of each Anchor Task. Find tips to launch tasks, support all students, and synthesize new learning. Download a sample.

### Problem 3

Make a friendly number to solve.

a.389 - 57 = _____

b.771 - 98 = _____

#### Purpose

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#### Facilitation Guidance

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## Problem Set

15-20 minutes

Give your students more opportunities to practice the skills in this lesson with a downloadable problem set aligned to the daily objective.

## Target Task

A task that represents the peak thinking of the lesson - mastery will indicate whether or not objective was achieved

5-10 minutes

Make a friendly number to subtract.

a.600 - 190 = _____

b.510 - 97 = _____

c.450 - 298 = _____

d.493 - 65 = _____

#### Student Response

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## Additional Practice

Daily Word Problems, Warm Ups, and Center Activities are aligned to the content of the unit but not necessarily to the lesson objective, therefore feel free to use them anytime during your school day.

### Word Problems and Fluency Activities

Word Problems and Fluency Activities

Help students strengthen their application and fluency skills with daily word problem practice and content-aligned fluency activities.

Lesson 12

Lesson 14