More on Multiplication (3rd Grade)

As I mentioned on my about me page, I was a fourth grade teacher for 3 years, but I did my student teaching in 3rd grade.  We are going to continue looking at the 3rd grade standards for Multiplication.

The next standard we are going to look at is one that students often struggle with.  This would be a great skill for you to work on at home.  You can use some of the same pictoral models that I showed you on the New Math Multiplication post.

3rd Grade Texas Standard

The student is expected to determine the unknown whole number in a multiplication or division equation relating three whole numbers when the unknown is either a missing factor or product.

3rd Grade Common Core Standard

CCSS.MATH.CONTENT.3.OA.A.4
Determine the unknown whole number in a multiplication or division equation relating three whole numbers.

As you can see, the standards are very similar.  

Finding the Unknown

Product: The answer to multiplication problem.

Factor:  The factors in a multiplication problem would be the two numbers being multiplied together.

These are definitions that your child is going to need to know.  Quiz them and make sure that they know what they mean.

Finding the Unknown Using an Array

The first way that I am going to show you is with an array.  If you want to do practice problems at home, I am going to tell you how to set them up.  

Example 1.  You can start by choosing any simple multiplication problem.  In 3rd grade, the focus will be on multiplication within 100. (Meaning the answer should be 100 or less)  What this problem is asking your child to do is complete the array.  They know that there are four rows in this array, but they need to be able to determine the number of columns.  Have your child continue adding dots until they get to 20.  Make sure that they do not forget to count the first 4 dots, and make sure that they add one at a time to each row.  (They should have equal groups.)

Finding an Unknown Using Equal Groups

This method of finding the unknown number is very similar to using an array.  Here is another way to set up a practice problem to find the unknown.

In the picture above, I provided two examples on how your child can do equal groups.  The first one is asking the students to place the 20 dots into the 4 circles evenly.  Your child should be taking one dot at a time and adding them to each group until they get to 20.  The answer will then be, how many dots are in one of the circles.  

For the second problem, you gave them the number in each group.  This time your child needs to circle groups of 4 until they do not have any dots left.  They can then count the number of groups of 4 that they have.

Finding an Unknown Using Strip Diagrams

In this strip diagram, your child will have to recognize that the number 20 is being split into 4 groups.  This is where knowing your math facts comes in handy.  If your child knows that 4 groups of 5 make 20, this problem will be very simple for them.

Finding an Unknown Using the Equation

I will probably say this in almost every post on this blog, but only because it is so important.  YOUR CHILD NEEDS TO MEMORIZE THEIR MATH FACTS.  If your child knows their math facts, then they will be able to look at 4x?= 20 and know that ?=5.  Practicing math facts is a great thing to work on at home with your child.  When I was teaching, I would have my students do Math Minute Challenges.  They would try to answer as many basic multiplication facts as they could in one minute.  We made it a game, and they loved to compete against each other.  You can find Math Minute Challenges to do at home on google or you can write your own problems.

I hope that this post will be helpful for you when working with your students at home.