Use Number Line for Subtraction

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Objective

SWBAT solve subtraction equations within 20 using a number line.

Big Idea

My students have learned to identify missing numbers on a number line. Now I want them to see a number line as a tool to solve subtraction problems.

Rev Them Up

5 minutes

I will have my students play a game of "Around the World."

Directions: This is a competitive game to see who can say the correct answer first.  You begin by selecting two students.  These students stand up and you will ask your question.  Whoever says the answer first, wins.  The winner is then matched with a new person and the same process proceeds.  You will continue to match the winner with a new person until everyone in the room has a turn and the final winner is produced. I love this game because it can be used in any content area. Go here to see a video of my class playing the game to compare numbers.

Today's lesson will review subtraction and work towards building fluency in solving subtraction equations, which correlates with our common cores standards for first grade. (1.OA.C.6). For this game I will have my students answering questions towards "simple subtraction facts." Watch the video in the resource section...they love this game!

Examples:

Okay, here we go, what is the answer to?

2-2=

3-1=

5-2=

Continue with numbers like this until everyone has a turn.

Whole Group Interaction

15 minutes

I have my students play a game every so often called Cross the Line (you can go to the Rev Them Up section here to see that game in action). I use masking tape at the beginning of the year to create the line needed across our carpet for that game. This line is going to come in handy when playing today's game, too. I will create a life size number line for my students to stand on and use. A number line is a very important mathematical tool that I want my students to use and find its value in different circumstances. (MP5). They can use a number line in many ways but for this lesson it will be to investigate subtraction. In the past, they have used it to discover missing numbers, to develop their rote counting skills, and to identify patterns in number counting.  

It is easy to build a life-size number line. You can use calendar numbers, hand-write numbers, or type numbers to lay across the tape. Try to space them out equally and place the numbers 0-20 across the tape. You can look at the pictures in the resource section of my class number line.

I will pick different students to help me solve different subtraction problems. I want them to learn to start on the first number (minuend of the problem) and jump backwards (to the left) for the second number (subtrahend). The number they land on is the answer (difference) for the problem. If my class can stay focused, I will try to do a problem with every student. 

Independent Practice

10 minutes

Need: Print the Number Line Subtraction Worksheet and copy for each student.

It is time for my students to practice subtraction using their own number line. I have had my students make their own number line in previous lessons and I also purchased a name plate for their desk at the beginning of the school year that supplies a number line.  If you buy name plates, and they do not contain a number line, they can also use a ruler if there is one printed on the name plate.

I will walk the room and watch my students as they solve their problems to help support around two potential misconceptions. It is common for students to move their finger as they jump backwards, but their counting may not match up. This is one potential misconception. They may also count the starting number instead of the jump, which is a second potential error. Though we went over these during the whole group portion of the lesson (and hopefully getting their whole body involved in the process helped solidify the correct way to use the number line), I do want to catch these areas of challenge in the process so that students can learn from them.

Closure

5 minutes

I will ask my students to turn to a partner and describe how to use a number line to solve a subtraction problem.

They can use the following problem as an example: 9-7=2