Review: Multiplying a 2-Digit Number by a 2-Digit Number

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Objective

SWBAT multiply using the expanded algorithm to find partial products, then add to find the product.

Big Idea

Students can use place value to multiply by finding partial products. The partial products are added to find the product.

Whole Class Review

10 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 multiplying a 2-digit by 2-digit number using the expanded algorithm.  This aligns with 4.NBT.B5 because the students are multiplying two two-digit numbers using strategies based on place value.  Because this is a review skill, I give the students a brief lesson on multiplying using the expanded algorithm.

To review the skill, I display the Expanded Algorithm.pptx power point on the Smart board.  The students are at their desks with paper and pencil.  They work the problem as I work it on the Smart board.

Problem:  32 x 17

Identify the ones place and the tens place to help with writing the 4 simpler problems to multiply.  To do this, I place the numbers in a box.  I write ones and tens over the correct place.

 Tens Ones 3 2 1 7

Next, write your 4 simpler problems based upon the place value.

2x 7 = 14

30 x 7 = 210

10 x 2 = 20

30 x 10 = 300

Add the partial products to get a product of 544.

Independent Practice

15 minutes

The students will practice the skill independently because they will have to work alone for the state test.  Each student is given a Multiplying a 2-digit by 2-digit.docx handout.  They must solve the problem by using the expanded algorithm.  Then the students must select the correct multiple choice answer.  (Our state test is a multiple choice test.  It is important that the students practice selecting the right multiple choice answer.)  The students must place the problem in the place value chart.   In the Video - Multiplying a 2 digit number by 2 digit number.mp4, you can see what is required of the students.

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 them to the answer.

Possible Questions:

1.  What is the value of each number?

2. After you find the 4 partial products, what must you do next?