# Lesson: Bar Model, Day 2

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### Lesson Objective

An introduction to the bar model as a means for solving addition and subtraction number stories. Today will focus entirely on subtraction for take away problems.

### Lesson Plan

Edward W. Brooke Charter School

Unit: Add and Subtract within 100

Lesson: 2.2

Teaching Point: An introduction to the bar model as a means for solving addition and subtraction number stories. Today will focus entirely on subtraction for take away problems.

Materials:

• Bags of linking cubes (same ones used in yesterday’s lesson)
• 2.2 Independent Practice Sheet
• 2.2 Math Workout
• Slates and Markers

Counting (15 minutes)

• Refer to 2.2 Problem Solving Task
• FOR THIS PROBLEM SOLVING TASK, STUDENTS WILL NOT BE USING THEIR PROBLEM SOLVING KITS. INSTEAD, THEY NEED TO USE THE BAGGIES OF LINKING CUBES THAT WERE USED IN LESSON 1.13.
• Send students off to work independently

Teaching (20 minutes)

• Have students turn and talk about how they used the linking cubes to solve the problem solving task.
• Have a whole group discussion about how students used the linking cubes to solve the problem solving task.
• Important points to include in this discussion:
• We started with a whole/total (12 cars, 12 linking cubes in a train) and we took away part (the 9 cars that drove away).
• We started with a number and ended up with a number that was less.
• We made a bar of linking cubes and then we took part of that bar (a certain number of linking cubes) away.
• Explain to students that we can make a bar model (they should know this term from yesterday) that looks very similar to what we did with the linking cubes that can also help us solve this number story. Remind students that we will be using bar models to solve number stories throughout the rest of the year.
• Show students what the bar model should look like when we are doing subtraction as take-away problems.
• You might want to show this problem with linking cubes to show that you start with a total amount of one thing, you take away part, and you are trying to figure out how many are left.
• Let’s try it out! As a whole group, solve the following number story using the bar model. Read the problem to the students. Have the students read the problem aloud twice. Have the students draw the bar model that mathematicians can use to solve this problem.
• There were 13 cookies sitting on a plate. Ms. Auritt ate 4 of the cookies. How many cookies are left?
When you have discussed the bar model as a whole class, have the students write a number sentence that describes what is happening in this number story. Discuss the number sentence as a whole group.

Independent Practice (10 minutes)

• See 2.2 Independent Practice Sheet.
• Read word problems to students. Have the students read the word problems aloud twice.
• You might want to keep students on the rug for this independent practice since this is their first day working with this concept.
• The work that students produce will be a great way to assess whether or not students understand how to use a bar model to solve subtraction as takes away number stories.
• You might want to provide students with linking cubes that they can use to help them figure out how to set up the bar model.
• Collect the students’ work and go over the problems as a whole class.

Math Workout (10 minutes)

• Review any standards not yet mastered; see 2.2 Math Workout.

Summary

• By the end of this lesson, students should understand how to make a bar model for a subtraction as take away number story.

### Lesson Resources

 2.2 independent practice sheet.docx   Activity 360 2.2 math workout.docx   Activity 253 2.2 problem solving task.docx   Activity 225