Change Unknown Word Problems with Number Lines

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SWBAT use a number line to solve a change unknown word problem.

Big Idea

Students solve change unknown story problems using a number line. This lesson gives students a new strategy to attach change unknown word problems.


10 minutes

Today we are going to work on solving story problems using number lines.  In order to do this, we are going to build a human number line. 

I have 11 students come forward and have them hold boards with the numbers from 0-10 written on them. 

I then pose a question:

Jha’Kyla has 8 necklaces.  She gives some of them to Jayda.  Now she has 3 necklaces. How many necklaces does Jha’Kyla have now?  

We “Act out” the problem using the human number line (starting at 8, moving five down and ending at 3).  We "act out" the problem by demonstrating moving down the number line by counting the "jumps" out loud as we move down the number line. 

My students have had experience with number lines before but I chose to have students build a human number line so that they could visualize the process of making "jumps" on a number line. 

Introduction to New Material

10 minutes

We can use number lines to help us understand story problems.  I am going to give you a number line and I am going to put a story problem on the board.  We are going to use the number line to help us solve this problem. 

Problem of the day:

Jason has 19 hamburgers.  Dylan comes and takes some hamburgers.  Now Jason has 7 hamburgers.  How many hamburgers did Dylan take?

I hand out the number lines to 20 in sheet protectors (the number lines have ticks on them but are unnumbered) and have students work to set up and solve the problem using the number line. (I chose to give students an unnumbered number line so that they can use it for a variety of different numbers.)

When finished, I have two or three students share out their work.  As they share, I make sure that they are (1) labeling the number line correctly and (2) using the number line accurately. 

I put another problem on the board and have students solve it using the number line.

Alton has 17 oranges.  His sister comes and takes some of his oranges.  Now Alton has 6 oranges.  How many oranges did his sister take?

Guided Practice

15 minutes

Now that we have solved problems as group, we will spend about 5 minutes working on our own to solve a number line problem.

As students work, I check for accuracy/trends.  When finished, I bring students back together and have them share their work using a number line on the Promethean board or a number line on an anchor chart.

OPTIONAL:  Students can use beans or counters on the number line to help skip count.  This tool allows students to to concretely model a problem and the number of "jumps" in the problem. 

Independent Practice

15 minutes

During independent practice, students will work independently on two problems using a number line. 

 As students work, I will circulate to determine trends and help students who have misconceptions.  



5 minutes

We are going to share our answers to our first independent practice problem with a partner.  As you share, you can use these sentence starters:

I solved my problem by...

This is how I used my number line...

I started by...

As students share, I circulate and listen to conversations.  If time permits, I have two partners share their work underneath the document camera, explaining their strategy and how they used their number lines.