Review: Multi-Digit Subtraction

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Objective

SWBAT subtract with and without regrouping by using a place value chart.

Big Idea

Place value charts can help students subtract.

Whole Class Review

15 minutes

In review lessons, I like to use various strategies to revisit the skill.  Because it is a review skill, there is not a lot of conversation between the students.  The purpose of the review before the state test is to prepare the students to work independently in order to be successful on the end of year assessment.

 

In today's lesson, the students review subtracting whole numbers using a place value chart.   This aligns with 4.NBT.B4 because the students are subtracting using the standard algorithm.

The students are sitting on the carpet in front of the Smart board.  (I like for my students to be close so that I can make sure that all of them are being attentive.)  To review this skill, I show the students a scholastics interactive video at the following site:

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

Because this is a review skill, I give the students a brief lesson on subtracting using a place value chart.

Problem:  

245 - 92 =

To give the students a conceptual understanding, I use a place value chart to model subtracting.  I remind the students that when they are subtracting multi-digit numbers, they should line the numbers up according to place value, then subtract vertically.  

Hundreds

Tens

Ones

2

4

5

 

9

2

 

 

 

 a.  253

 b.  153

 c.    53

 d. 143

With the students help, I model subtracting a multi-digit number with a place value chart.  I let the students know that we begin subtracting in the place farthest right.  In this particular problem, we begin with the ones place.  I ask the students, "What is 5 take away 2?"  The students know that it leaves 3.  Next, we move to the tens place.  Because I know that this place will need to be regrouped, I want the students to understand completely.  Therefore, I ask, "What is the value of the 4 in this place?"  The students know that the value is 40.  I ask, "What is the value of the 9?"  The students know that the value is 90 because it is in the tens place.  I ask, "Which is larger 40 or 90?"  The students know that 90 is greater than 40.  I tell the students that because 90 is larger than 40, we must regroup.  I ask, "What is the value of the 2 in the hundreds place?"  The students know that the value is 200.  I explain to the students that because I cannot subtract the tens place, I must regroup by taking 100 away from the hundreds place.  I model this by changing the 2 in the hundreds place to a 1.  I place a 1 in front of the 4 in the tens place to get the number 14.  I explain to the students that now we have 14 tens.  I ask, "What is the value of 14 tens?"  Some students yell out 140.  I model how to subtract 9 tens from 14 tens.  It leaves us with 5 tens.  Last, we have 1 in the hundreds place.  The answer to the problem is 153. (The students will not be able to use place value blocks on the state test.  Therefore, I do not use them in this lesson to explain regrouping in subtraction.  This lesson is strictly on using the place value chart to subtract.  The students must understand when to regroup based upon the value of the numbers.  Because the students will have scratch paper, they can draw their own place value charts on the state test to help with solving these problems.)

 

Independent Practice

20 minutes

The students will practice the skill independently because they will have to work alone for the state test.  Each student is given a Multi-Digit Subtraction Review.docx-1.docx.  They must solve the problem by using the place value chart.  Then the students must select the correct multiple choice answer.  The students must show their work by regrouping if it is necessary.   In the sample Video - Review Subtraction.mp4 of student work, you can see how the students solved the problems.

As the students work on the problems, I walk around to monitor their level of understanding.  If the students are having a difficult time, I will ask guiding questions to help lead the students to the answer.  

Possible Questions:

1.  What place should you begin subtracting?

2.  Do you need to regroup? If so, explain how you should do it.

3.  How can you check your answer?

Any students having difficulty with the task will be grouped for intervention.

Share/Discuss/Analyze Solution(s)

15 minutes

Upon completing the independent practice, I call the students back together as a whole.  I feel that it is very important to close out the lesson by sharing answers.  By doing this, it allows the extra opportunity to reach any students that still do not understand the concept.

I call on students to share their answers.  All students are not auditory learners; therefore, it is very important for the students to see the examples of work (Student Work and Student Work).  I use my document camera to display the student work on the Smart board.  

Students are allowed to ask questions during this closing of the lesson.  The most important aspect for me is that I have identified any students that need 1-on-1 or small group remediation.