Unit 3 Math – Multiplication Strategies

Hello everyone,

Over the past few weeks we have been working on several different strategies for multiplying, specifically multiplying 2-digit by 2-digit numbers. We will be finishing this unit today (November 24th), and we will review after Thanksgiving weekend, before their assessment. To help with this review, Mr. Moss and I thought it would be helpful to post some videos of the different strategies.

The first lesson was to estimate numbers before multiplying them so that you can just multiply the basic math fact and then add the zeros at the end. Here is a video to help explain that a bit better:

https://www.khanacademy.org/math/arithmetic/multiplication-division/multi_digit_multiplication/v/multiplying-whole-numbers-and-applications-4

The next day, we worked on using the area model to actually do 2-digit by 2-digit multiplication. Think of taking a rectangle are breaking it apart into parts, finding the area of each rectangle and then adding it all back together. Here’s another video for that method:

https://learnzillion.com/lesson_plans/6075-use-an-area-model-for-multiplication-of-two-digit-numbers-by-two-digit-numbers#

After that, we worked on using partial products to multiply. Basically, doing the same thing as the area model, but without the box. Here’s a picture to help:

And, of course, another video to help:

https://learnzillion.com/lesson_plans/6125-solve-2-by-2-digit-multiplication-problems-using-partial-products

Finally, we got to the standard method of multiplication. We started by looking into why this method works, something even most adults are unsure of. We broke apart the multiplication problem again, but instead of breaking into four parts like with the partial products method, we broke it into two. Students know how to do 2-digit by 1-digit multiplication well by now. They also know how to multiply 2-digits by 2-digits as long as one of the numbers ends in a zero. So we took apart the bottom number, for example:

23        became       23    and   23

x 34                          x 30           x  4

Students can much more easily do 23 x 30 and 23 x 4 than they can do 23 x 34.

Once they found the answer to both parts of the broken up problem. We added them together.

Finally, we learned how to do it all together – the same way we all learned – with regrouping numbers. Here’s a video to better explain that (2-digit by 2-digit with regrouping starts at 3:20)

https://www.khanacademy.org/math/arithmetic/multiplication-division/multi_digit_multiplication/v/multiplication-5-2-digit-times-a-2-digit-number

We want students to be familiar with all 3 methods of multiplication, but they can use whichever method they like best when doing multiplication from here on out. Today, we discussed how everyone has different preferences when it comes to math and that it’s ok for them to pick their favorite method when doing multiplication.

Hopefully this wasn’t too confusing for everyone; it’s harder to explain in writing than it is in person. But the videos should do a pretty good job of giving a visual to my rambling.

Enjoy!

~ Mr. Walmer

 

Posted in Class Updates|By Brendan Walmer