Adding Decimals

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The students will be able to add numbers with decimals.

Big Idea

Bringing down the decimal for big savings!


10 minutes

Today’s lesson is the first in a four part series of lessons using coupons to assist in solving problems with numbers that include decimals.  Each lesson will focus on a different operation with decimals; adding, subtracting, multiplying, and dividing.  Coupons are a great way to make a real world connection to the math.

I begin by focusing on how to add numbers that include decimals.  I show the students a short youtube video that highlights the process of adding decimals. 

When the video is finished I have students discuss the video in their groups and determine the key components of adding decimals.  I ask them to create a small poster centered on adding decimals.  After about five minutes I bring the students back and have them share out their thinking and posters. 

My goal is that students are able to identify the key components of adding decimals as lining up the decimal and bringing the decimal down into the answer.  During the group share out I guide thinking if students are struggling with the concept. 


20 minutes

To prepare for using coupons in this lesson and the next four lessons I collected the coupon section from a few weeks of the Sunday newspaper and asked a few colleagues to bring theirs in as well.  I had one coupon section for each of the six groups in my room.

Before passing out one section to each group I explained the upcoming activity to them.

Okay today were going to start an activity that is using coupons.  We are going to cut out our coupons today and then add up the savings we would have if we purchased these items and used the coupons.  While working in your groups you need to cut only 10 coupons total.  The coupons can be for whatever items you would like to “purchase” when you go to the store. 

When preparing for this activity and looking through the coupon sections I noticed that the majority of coupons were for save $1.00 or save $2.00.  This kind of slightly defeated the purpose of the activity which was to add decimals so I adapted the coupons a little.  Once the students had chosen their coupons I had them change the amounts on the coupons.  If the amount to save on their coupon was an even dollar amount I had them change it.   

I show the students an example coupon on the document camera.  The coupon is for save $1.00. 

Look at this example of a coupon.  Many of your coupons will be similar to this in that they say save $1.00 or $2.00.  Since we are practicing adding decimals we are going to make this a bit more challenging for ourselves.  Once you have chosen your ten coupons, I would like your group to use a sharpie to change the price of the coupon by adding value to the tenths and hundredths.  Here are some options you can use. 

I put up five examples of decimal endings on the board for students to choose from; .05, .35, .40, .75, or .85.  I change the value of the displayed $1.00 coupon to $1.85. 

You can use one of these options to add value to your tenths and hundredths or something similar.  I am going to give you about five minutes to cut out your ten coupons and change the prices.  When your group is done you should have ten coupons in the middle of your table with adjusted prices. 

After allowing students time to work I bring the students back and explain the next step of the activity.  I tell them now we are going to calculate the total cost of savings we would have if we used these coupons.  I give the students each a sheet of construction paper and tell them they need to show all their work while getting the total amount of savings.  I set my expectations that each member of the group needs to be actively participating in the creation of the work.  I also tell them that each group will be presenting their work at the end of ten minutes and explain their method of calculating the total savings.  I circulate the room and guide the students as needed.  I have students share their work on the document camera and present as a group after allowing them time to work.


20 minutes

I have students save their coupons and savings calculations in their math folders for use in tomorrow’s lesson.  To wrap up this activity I give the students a worksheet that requires them to add to numbers that include decimals.  I have them complete this individually and turn it in as an exit slip.

I would like you guys to work on this sheet individually for about ten minutes.  I want you to focus on showing your work for each problem.  So, even if you don’t get finished I can look at the work for the problems you did complete to see if your process is on the right track.  Before we get started let’s remind ourselves of the key components of adding decimals.  What are they?

I ask students to respond as I listen for them to identify lining the decimals up and bringing the decimal down as the key components.  Students work for about ten minutes on their own and I answer questions as needed.