Use Models to Add

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Objective

SWBAT use concrete models to add ones or tens to a two-digit number.

Big Idea

In this lesson, students begin to add two digit numbers by drawing models to represent the tens and ones place.

Activating Strategy

10 minutes

I like to start this lesson by watching the following video:

I then call out a two digit number and have the students use base ten blocks to model the number.  After modeling the number, I have the students record their work using a quick drawing.  Sketching quick pictures gives a students a strategy that is easy to use because drawings are concrete and can be made quickly and simply.

Tell students that they will use their quick drawings to help them visualize addition and subtraction problems.  They can also use quick pictures as a way to check their computations.

In first grade it's important for students to begin to experiment with representing problem situations in multiple ways including numbers, words, drawing pictures, using manipulatives, acting out, etc.  By having the students learn to draw a picture, it will help to make the connection between concrete ideas and abstract ideas.  (MP4)

After children model problems using base-ten blocks, they then record their work by representing the model they made. Quick pictures provide a way that is easy to use because the drawings can be made quickly and simply. Children should be encouraged to make simple representations for the base-ten blocks.

When you first introduce quick pictures, explain that these drawings will be used to record the work children have done with base-ten blocks. Point out that it is important to make accurate drawings of the number of tens and the number of ones used, but that it is not important that the drawings look exactly like the base-ten blocks. Have children practice drawing lines and dots to represent tens and ones until they can do this easily and efficiently.

Tell children that they will use their quick pictures to help them visualize addition and subtraction problems. As they build their number and operation concepts, they may stop using the base-ten blocks to model the problems and use quick pictures as a pictorial model instead. They may also use quick pictures as a way to check computations.

Teaching Strategies

15 minutes

Write the number 26 on the board.  (also available as a PPT Use Models to Add)  

Ask students: How can we use tens and ones to show 26?

I like to tell students that in today’s lesson, we will learn how to draw a model that will help us add a two-digit number.  I then read or write on board/chart paper the following problem:

Sam counts 24 cars as they go by.  Then he counts 5 more cars.  How many cars does Sam count in all?

 Ask the students:

  • How can we draw a picture to show the addends?  (I can draw 2 lines to show 2 tens, and 4 circles to show 4 ones.  Then I can draw 5 circles to show 5 more ones.)

I then model to show how I add the tens with the tens and the ones with the ones.  The key to this lesson is to teach them to add the ones place first. 

Write the problem 32 + 4 on the board.  Ask the students:

  • Do you need to add tens to find the sum? Why or why not?  (No.  There are only 4 ones to add to 32, you can just add the ones to find the sum.)

Have a student come and model how to draw the tens and ones to solve the problem.

Write the problem:  32 + 40 on the board.  Again, have a student come to the board and model how to draw the tens and ones to solve the problem.  

The key to this lesson is to get the students to learn to add the ones place first.  This is important because in second grade they will to add and subtract using regrouping.  If they don't learn to add the one's first, it can potentially become a habit to undo when it comes to regrouping.

In this picture the student demonstrated how to group the tens and ones together in the picture before adding.

Independent Practice

30 minutes

I like to have students complete Use Models to Add_worksheet for the independent portion of this lesson.

For struggling students, have them use base ten blocks to solve their problems.  This will allow them to further understand the concrete portion of this lesson.

Closing/Summarizing

5 minutes

To close out the lesson, I have students write a story problem in their journals about 40 apples and 17 bananas.  They are to draw a picture to show how they solved their problem.