Solving Subtraction Number Stories- Writing the Answer Day 1

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Objective

Students will be able to solve subtraction word problems using objects and write a numeral for the solution.

Big Idea

In order to share the answer to a word problem, it is common practice to write a numeral as the solution to the problem. In this lesson, the students will keep practicing using manipulatives to solve subtraction word problems but will also write the answe

Problem of the Day

5 minutes

I start each math lesson with a Problem of the Day.  I use the procedures outlined here on Problem of the Day Procedures.

Today's Problem of the Day:

There were 10 ants at the ant hill.  When it started to rain, 3 ants washed away.  How many ants were left?

I set this problem up with some structure to help the students organize their thinking.  I put an ant on the Notebook file with infinite cloner turned on so that the students can use it to represent the problem.  If you do not have a SMART Board, you can use the PDF and have the students draw pictures or use manipulatives.

Since we do this whole group, I have one students come up and do this problem.  I remind students to check their work when they are finished and have the class tell if they agree or disagree by showing a thumbs up or thumbs down.  


 

Presentation of Lesson

25 minutes

Today I am going to tell you some more stories.  Each story ends with a question.  We are going to again use the cubes to answer the question at the end of each story.   Stories like this that include a math problem are called word problems.  While I tell you the story, use the cubes to show what is happening in the story.  When we solve these kinds of problems, we usually don't just tell someone the answer, we write it down so that we remember it and other people can look at it.  Today you are going to record the answer to our word problems on your paper.

 

I give each students a Word Problems Worksheet I follow our Paper Procedures to distribute the papers.  I also hand each student a cube train containing 10 cubes.  I tell students that when they get back to their seats they need to take the cubes apart and lay them beside their paper.  When they have done that and put their name on their paper, then put their hands on their head.

 

I say the following word problems aloud.  As I say them, I model on my mat using the cubes and have the students model the problem on their mats.  I ask for a student to orally give me the answer by raising a quiet hand.  We then write down the answer on the line.  I still want the students to focus on listening to the problem and using the cubes to find the answer, but I want them to start to get used writing the answer to a word problem.  The process is just as important as whether the students get the correct answer.  The students need to use several of the mathematical practices to do this.  They need to make sense of the problem and engage in finding the answer (MP1).  They need to use the cubes to model the problem (MP4), and they need to use the cubes as math tools (MP5).  At this level, cubes and other manipulatives are math tools that students need to learn to use appropriately to solve problems.  See example here.

 

Sarah has five cookies.  She eats two cookies.  How many cookies does she have left?

Fred has eight toy cars.  He gets gives three cars to his brother.  How many toy cars does Fred have left?

Bella has five Barbie dolls at home.  She lost two of them.  How many Barbie dolls does she have have left?

Chris gets ten lollypops from his grandmother.  He eat one of them.  How many lollypops does he have left?

 

When we are finished, I ask each student to put their cubes back together into a train.  They need to count and make sure that they have 10.  They then need to make a pile of papers and cube trains in the middle of their table.  I select one student to collect the papers and another student to collect the cube trains.  When students are finished I call one representative from each table to come back and get the center for their table.  All students start their center at the same time today.

Practice

20 minutes

The centers for this week are:

 

I quickly circulate to make sure students are engaged and do not have any questions about how to complete the centers.  Because of the trouble during our addition unit, I decided not to introduce any subtraction centers this early in the subtraction unit. 

I pull 3 groups (5-10 minutes depending on need).  We do an activity similar to the whole group activity.  I have the students use bears and fruit counters instead of cubes to show that we can use a variety of manipulatives to represent the information in a number story.

Prior to clean up, I check in with the other tables to see how the centers are going.  My students have been struggling with getting cleaned up quickly and quietly after centers.  Lately I have been using counting down from 20 slowly instead of a clean up song.  Counting backwards is as critical as counting up. Students need to be able to know the number that comes before, as well as after, any given number (w/i 10, w/i 20, etc.). Counting back is a critical strategy for subtraction.

The students like to count backwards with me as they clean up and I can lengthen or reduce the clean up time based on how students are doing and how much time we have.

Closing

5 minutes

To close, I put one student's paper on the document camera a project it on the SMART Board and have that student show a subtraction word problem and explain their work.  I mention positive things noticed during centers as well as something that needs to be better next time. 

I review what we did during our whole group lesson.  "Today we learned about solving problems that come from a story.  These are called word problems.  We also started writing the answers to these problems.  Tomorrow we will be continuing to work on word problems, and we are going to keep writing the answer to the problems."