Subtracting Whole Numbers

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Objective

SWBAT subtract numbers to thousands with and without regrouping.

Big Idea

Using place value helps make subtracting easier.

Opener

5 minutes

In this Subtracting Whole Number Introductory Video, I explain the lesson for today.

This lesson allows the students to subtract whole numbers with and without regrouping.  Students must be able to subtract in their every day lives.  To capture the students attention, I set up a scenario that gets them to thinking.  "Tim was very good at saving money.  One day while he was driving home from work, his car had a flat.  Tim had to use some of his money from his savings account to buy a new tire that would cost $128.  Tim has $452 in his savings account.  How much money will Tim have left after he buys a new tire?"  Who knows which operation we can use to solve this problem?  I call on a student to give you the answer to the question.  To student responds, "Subtraction."  I let the student know that he is correct.  I tell the class, "We must use subtraction to find out how much money Tim will have left.  Today, we use place value blocks to help us with our subtraction."

Direct Instruction

10 minutes

Before we begin the lesson, we review the things we have already learned about place value.  This is very important when subtracting with regrouping.  I remind the students that the highest digit that can go in each place is a 9.  Also, each place is 10 times larger than the place to the right.  Reminding the students of these things will help prevent misconceptions during the lesson.

The students are seated at their desk during this direct instruction lesson.  I want the students at their desks because they will be participating in the hands-on instruction as I discuss subtracting whole numbers.  The students have a sheet of paper, pencil, place value chart, and base ten blocks on their desk.  The students use the place value charts and blocks to help with the subtraction as they work it with paper and pencil.

I use the Subtracting whole numbers power point to direct the instruction.  

"Tim had to use some of his money from his savings account to buy a new tire that would cost $128.  Tim has $452 in his savings account.  How much money will Tim have left after he buys a new tire?“  The students should use the base ten blocks and place the numbers on the place value chart.  Also, the students should write the problem down on their paper.  I remind the students to line their numbers up according to place value.  

As I go through the power point, the students get a conceptual understanding of subtracting with regrouping by using place value blocks.  

 As I go through the lesson step by step with the power point, I like to catch all misconceptions before the students get into groups to do their activity.  Therefore, I address all possible misconceptions as I discuss the lesson.

Possible Misconception(s):

1.  When regrouping, forgetting to take away 1 from the place to the left.

Questions that I ask during direct instruction to help the students avoid making them during group activity.

1.  Is the top number larger than the bottom number?  If so, how do you regroup?

2.  How did the ones place go up by ten?  Where did you get the ten?  Did the number in the tens place change?

Group or Partner Activity

20 minutes

To let the students practice the skill, I put the students in pairs.  I like for my students to work in very small groups because it allows me the opportunity to hear what they each are saying.  It also gives them a chance to lend their voices easily.  

This activity requires the students to continue using the place value charts and blocks to subtract.  They use a Subtracting Whole Numbers Group Activity activity sheet of word problems to practice the skill.  The students must communicate with each other as they solve the problems.  They must come to a consensus that their answer is correct before moving to the next problem.  This requires the students to critique the reasoning of their classmates.  

As the students work on the problems, I walk around to monitor and listen in on the conversation.  I interject with questions as needed to lead the pairs to the conceptual understanding outlined for the lesson. 

 

Early finishers can go to the computer and get additional instruction at the following site:

http://studyjams.scholastic.com/studyjams/jams/math/addition-subtraction/sub-with-regroup.htm

 

Independent Activity

10 minutes

After the students complete their partner activity, I let the students practice the skill on their own.  This allows me to assess their individual understanding of the concept.  The students continue working with the place value charts and blocks.  I give each student a handout (Subtracting with Whole Numbers Independent Assignment) of the problem to solve.  The place value blocks are used to help the students solve the problem.  They must be able to model regrouping with the place value charts.  

I walk around and monitor as the students work.  This is another opportunity for me to give that one-on-one feedback or instruction to the students that need it, as is evident in the Video - Subtracting Whole Numbers.

Problem:

My little brother collects marbles.  He has a total of 278 marbles.  His friend, Pete, decided he wanted to collect marbles also.  My little brother gave Pete 39 marbles to help him get started.  How many marbles does my little brother have now?   

Closure

10 minutes

To close the lesson, I bring the class back together as a whole.  I call on a student to present their answer to the class.  Because this is another teaching opportunity, I model with the interactive place value blocks on the Smart board as the students explain their steps.    

Students have the opportunity to ask questions of me and their classmates during this part of the lesson.