Subtraction With Larger Numbers

Learning Resource Type

Learning Activity

Subject Area

Mathematics

Grade(s)

Overview

In this before activity, students will engage in a number talk to link strategies used with numbers within 100 to numbers within 1,000. The number talk uses numbers under 120.

This activity was created as a result of the ALEX Resource Development Summit.

Phase

Before/Engage

Mathematics (2019) Grade(s): 2

MA19.2.12
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.

Vocabulary

Compose
Decompose

Knowledge

Students know:

how to count to 1,000.
how to identify hundreds, tens, and ones.
how to compose numbers.
how to decompose two digit numbers.
how to record strategies for solving addition and subtraction problems.

Skills

Students are able to:

add and subtract within 1000.
model addition problems using visual models.
record strategies for solving addition problems.
communicate the relationship between models and symbolic (numeric) representations.

Understanding

Students understand that:

relationships between models of addition/subtraction problems and written strategies of those models can be used to justify solutions.

Learning Objectives

The students will use strategies based on place value and the properties of operations to subtract within 1000.

Activity Details

The teacher will download Google Slide Presentation: Subtraction with Larger Numbers.
Young students do not always understand that the strategies they use with smaller numbers work with bigger numbers. The numbers chosen in this activity are designed to encourage students to decompose the subtrahend in order to subtract in friendly parts.
The teacher and the students will read the learning targets together (Slide 2).
The teacher will gather the students together in a central location where the students can view a whiteboard, interactive board, or chart paper. The teacher will pose the following problems one at a time: 16 - 7 =? 56 - 7 =? and 116 - 7=?. The teacher and the students will follow the steps below: The teacher will pose a problem. The students will solve the problem in their head or mentally. When the students have an answer, they will place a thumbs up against their chests. The teacher will call on three students to share their answers. The teacher will record the students’ answers on the board. The teacher will call on three students to share how they solved the problem. The teacher will record their strategy on the board (Slide 3).
The teacher presents 16 - 7 = ? to the class. The teacher is ultimately looking for students to decompose 7 into 6 and 1.

16 - (6+1) = ? or 16 - 6 - 1 = ?

16 - 6 = 10

10 - 1 = 9

The teacher should model the students' strategies on a number line. The teacher may record students’ strategies in the white area on the slide, on chart paper, or on notebook paper under a document camera. Use the checklist/notes to record the strategies used (Slide 4).
The teacher presents 56 - 7 = ? to the class.The teacher is ultimately looking for students to decompose 7 into 6 and 1.

56 - (6+1) = ? or 56 - 6 - 1 =?

56 - 6 = 50

50 - 1 = 49

The teacher should model the students' strategies on a number line. The teacher may record students’ strategies in the white area on the slide, on chart paper, or on notebook paper under a document camera. Use the checklist/notes to record the strategies used (Slide 5).
The teacher presents 116 - 7 = ? to the class.The teacher is ultimately looking for students to decompose 7 into 6 and 1.

116 - (6+1) = ? or 116 - 6 - 1 = ?

116 - 6 = 110

110 - 1 = 109

The teacher should model the students' strategies on a number line. The teacher may record students’ strategies in the white area on the slide, on chart paper, or on notebook paper under a document camera. Use the checklist/notes to record the strategies used (Slide 6).
The teacher will review the strategies used with all three problems using the guiding questions on the slide. If no student decomposed 7 into 6 and 1. The teacher will need to ask, “How could decomposing 7 into 6 and 1 make 7 easier to subtract in this problem?” (Slide 7).

Assessment Strategies

The teacher will use the checklist/notes to record the strategies used.

Background / Preparation

The teacher will download Google Slide Presentation: Subtraction with Larger Numbers.
If the teacher plans to use chart paper and a chart marker, those items will need to be gathered.
Print the checklist/notes to record the strategies used.

https://docs.google.com/presentation/d/1XB9blrebCRAxunWl83N0uRfphPSuedCthH7Q3uP…

Approved Date

2020-08-06

Owner (Author)

jtowles