Multiplying by Multiples of 10 and 100

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Objective

SWBAT use basic multiplication facts and number patterns to multiply by multiples of 10 and 100.

Big Idea

Basic facts and place value patterns can be used to find products when one factor is 10 or 100.

Opener

5 minutes

In the Introductory Video for Multiplying by Multiples of 10 and 100, I explain the objective for today.  In today's lesson the students learn how to use patterns to find the product when multiplying by multiples of 10 and 100.  This aligns with 4.NBT.5 because the students multiply a whole number of up to four digits by a one-digit whole number, using strategies based on place value and the properties of operations. 

I let my students know that this lesson is important to them because they will use this skill a lot as an adult.  When they go shopping, they round their numbers to estimate the amount of money they spend.  

To get them interested in this skill, I review by getting the students to "sing and clap" the multiples of 10 and 100 with me.  Together, we clap and say 10, 20, 30, etc.  This should get the students excited about the lesson.  I explain to the students that the goal of today's lesson is to multiply by multiples of 10 and 100.  

Direct Instruction and Activity

40 minutes

I call the students to the carpet to begin the Multiplying by Multiples of 10 and 100 power point on Multiplying by multiples of 10 and 100.  This makes it easier on me to communicate and monitor all student participation as we go through the lesson.  I like for my students to participate in the discussion during direct instruction, so I call on various students or have choral responses at certain points of the lesson.

I let the students know that when they multiply by multiples of 10 and 100, they can use patterns to help them find their products.  The following problems are in the power point. I ask the students what is 3 x 40?  I give the students a few minutes to study the problems.

2 x 3 = 6
2 x 30 = 60
3 x 4 = 12
3 x 40=  ?

The students should be able to tell you that 3 x 40 = 120.  I remind the students that they can also use a visual model to help them. The number 40 is repeating 3 times. The students should know how to draw an array or groups to represent 3 x 40.

When you multiply by multiples of 100, you can use a pattern.  I ask the students to find the answer to 2 x 700.
2 x 7 = 14
2 x 70= 140
2 x 700 = ?

From the examples, the students should be able to find the product of 2 x 700= 1,400.

When you multiply by multiples of 100, you can multiply the 2 facts, then add 2 zeros.
For example,  2 x 7 = 14
Add the 2 zeros:  1,400
I ask, "Can anyone tell me why we add 2 zeros when multiplying by multiples of 100?
Why do we add 1 zero when multiplying by multiples of 10?"

I take volunteers to answer the questions.  I make sure that the students know that when you multiply by multiples of 10, youadd only 1 zero because the multiple of 10 has 1 zero.  Also, when you multiply by multiples of 100, you add 2 zeros because the multiple of 100 has 2 zeros.

Group Activity:

After the whole class direct instruction, the students practice the skill in groups.  I like for my students to work in small groups so that they all will have an opportunity to be heard.  

I put the students in pairs.  Each pair gets an Group Activity Multiplying by Multiples of 10 and 100. activity sheet.  The students work together to multiply by multiples of 10 and 100.

 

Early finishers can get more practice at the following site:

 http://www.studyzone.org/testprep/topic.cfm?TopicID=514

 

Independent Activity

10 minutes

To give the students an opportunity to practice on their own, I provide them with an independent activity (Independent Assignment Multiplying by multiples of 10 and 100).  It is similar to the group activity.  This gives me a clear view of which students have mastered the skill and which ones need remediation.

I put the independent assignment on the board for the students to see.  The students need a piece of paper and pencil to work this problem.  

 

Problem:

1.   6 x 7 = 42 

      6 x 70 = ____

       6 x 700 = ____

 

2.  3 x ___ = 150

3.  5 x ___ = 4,500

 

Closure

10 minutes

To close the lesson, I bring the class back together as a whole.  I like to end each class by going over the independent activity.  I call on a few students to share the answers to the problems.  I am mindful to allow time for questions from students who did not quite master the skill.

This is a good opportunity to have students summarize the lesson.  I call on various students to take the class through the steps of multiplying by multiples of 10 and 100.  I tell the students to be sure to include the patterns that helped them multiply by these multiples. 

Anticipated student responses:

I am listening for students to share that they multiplied the basic facts first.  Then, they counted the number of zeros.  The students should tell me that for multiples of 10, they added 1 zero.  Also, for multiplies of 100, they added 2 zeros.