Subtracting Money (Part II)

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SWBAT subtract money amounts.

Big Idea

In this lesson, students subtract using money amounts of $1.00 or greater.


12 minutes

At the beginning of class, students sit in a circle and I present a problem of the day: 

I want to buy a cookie for $.56 but I only have one dollar .  

I show students the one dollar bill.  

How much money do I get back? 

Turn to your partner and tell them how you think we should solve this problem. 

Students might suggest dividing the dollar into coins, subtracting $.56 from $1.00, or drawing tens and ones (dimes and pennies) to determine a total. 

Students might also suggest subtracting 56 from one dollar and subtracting across zeroes. 

I ask 2-3 students to share their ideas with the class, asking clarifying questions so that all students will understand their ideas. 

Introduction to New Material

10 minutes

In order to make the concept of making change concrete for students I model how to break a dollar into coins by taking the dollar bill away and using coins to build a dollar.  Then, I ask students to help me take $.56 cents away from the dollar, yielding my $.44 cents of change.  I made the dollar into two quarters, three nickels, three dimes and five pennies.  This breakdown allows the students to work with the coins in smaller denominations. 

Modeling this process helps students to understand what making change from a dollar really means--we  break the dollar, take some from the dollar and have a have the left over as our "change".

How could we show this problem using a number sentence or a bar model?

I hand students white boards and have them work in pairs to think about other ways to show this problem. 

As students work, I circulate and ask guiding questions:

1) Explain why  you set up your number sentence like that...

2) Is there another way that you could set up the number sentence?

3) is there a way you could solve this problem without a number sentence but with drawing (student might be able to draw the process that we just modeled using coin manipulatives)

After students are done working on this problem, I ask a few groups who have solved the problem differently to share their work. 

Some students might have set the problem up like: $1.00-$.56 = ________, which directly models the way that we worked out the problem using manipulatives.  Others might suggest $.56 + ______ = $1.00.  Others might draw a bar model and then use a subtraction problem while others might have drawn the coins to model the problem. 

As students share their strategies, I create a list on the board or an anchor chart so that students will be able to have visual anchor as they work on similar problems independently. 

Guided Practice

10 minutes

During guided practice, I divide my students into heterogeneous partners and have them work together to solve two problems involving subtraction. As students work, I circulate to support students.  

When students are finished working, I bring them back together and we go over the problems as a group. When we go over the problems, I invite students who did not share their strategies during the introduction to new material to share their work so that more students will get an opportunity to share and the class will get to hear more students' ideas. 

During the guided practice, students will have access to coin manipulatives and will be encouraged to break the dollar into smaller coins in order to model the subtraction process. 

Independent Practice

10 minutes

I tier independent practice based on students' understanding of this skill. 

Group A: In need of intervention

I work with this group to model and practice problems similar to the ones we worked on as a whole group and during guided practice. (Students in this group will have access to coin manipulatives if they want them) 

Group B: On level

I have students in this group work independently to solve problems similar to the ones we worked on as a whole group and during guided practice (Students in this group will have access to manipulatives if they want them). 

Group C: Extension

I have students in group C work independently to solve making change word problems with total amounts of $1.00-$5.00.

Exit Ticket

10 minutes

As a final check for understanding, I give my students an exit ticket which assesses their understanding of making change with total amounts of $1.00. 

As students work, I circulate but do not help students (I want to see how students can reason through these kinds of word problems without my assistance)

When students finish, I go over the exit ticket with them so that they can get immediate feedback on their work.