Lesson Video: Dividing by 8 Mathematics • 3rd Grade

In this video, we will learn how to use various strategies to divide by 8 within the known times tables up to 12 × 8, including using models and times table facts.

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Video Transcript

Dividing by Eight

In this video, we’re going to learn how to divide by eight using models, like arrays, and our knowledge of the eight times table. When we’re learning to divide by eight, it really helps to use the eight times table facts.

Let’s start by practicing the eight times table. One times eight is eight, two eights are 16, three times eight is 24, four times eight is 32, five eights are 40, six times eight is 48, seven eights are 56, eight times eight is 64, nine eights are 72, 10 eights are 80, 11 eights are 88, and 12 eights are 96. We call these numbers multiples of eight.

Let’s practice counting in eights one more time. Another way to multiply by eight is to skip count by eights. Eight, 16, 24, 32, 40, 48, 56, 64, 72, 80, 88, 96. Knowing the eight times table facts will really help us in this lesson when we’re dividing by eight. When we’re dividing by eight, one way to find the answer would be to divide 40 counters into groups of eight. Each of these groups contains eight counters. So, when we’re thinking about dividing by eight, we’re thinking about how many groups of eight there are or how many eights are there in 40. And there are five groups of eight.

One eight is eight, two eights are 16, three eights are 24, four eights are 32, five eights are 40. 40 divided by eight equals five. There are five equal groups of eight in our array. Which times table fact did we use to help us find the answer? It was five times eight. If we know that five times eight is 40, we know that 40 divided by eight equals five.

So, we can use models, such as our array, and our knowledge of the eight times table to help us divide by eight. Now that we’ve learned two ways to divide by eight, let’s try some questions.

Use the following diagram to calculate 56 divided by eight.

In this question, we’ve been shown a diagram or a model to help us calculate 56 divided by eight. We could call this diagram an array. An array is when we organize objects into equal groups. We know there are 56 balloons altogether, and we have to divide those 56 balloons by eight. The divisor, or the number we’re dividing by, is the number eight. We’re being asked how many eights there are in the number 56. So, the array shows us that 56 balloons are ranged into equal groups or rows of eight.

The balloons have been divided into groups of eight. How many equal groups or rows of eight balloons are there? In other words, how many eighths are there in 56? Let’s count them. Here’s one, two, three, four, five, six, seven. If we have 56 balloons and we divide them into equal groups of eight, there are seven groups. 56 divided by eight equals seven. We used the array to help us calculate 56 divided by eight.

This robot divides any number by eight and gives a result. In this case, the number 16 gives a result of two as 16 divided by eight equals two. What will the result be in the following case? 40 divided by eight equals what. And what will the result be in the following case? 64 divided by eight equals what.

In the first part of this question, we have to help the robot calculate 40 divided by eight. And in the second part of the question, we have to help the robot calculate 64 divided by eight. Did you notice that in all of the calculations we’re dividing by eight? How could we calculate 40 divided by eight? We could use an array and our knowledge of the eight times table to help.

When we’re dividing by eight, we can think of this as dividing a number into equal groups of eight. Here’s one group of eight, which gives us a total of eight. Two eights make 16. Three eights make 24. Eight, 16, 24. Four eights are 32, and five eights make 40. Eight, 16, 24, 32, 40. So, if the number 40 goes in and the robot divides it by eight, the result will be five. There are five eights in 40. 40 divided by eight equals five.

Now, we just need to answer the second part of the question. What is 64 divided by eight? How many eights are there in 64? Let’s keep on counting in eights. We already know that five groups of eight makes 40, so let’s just keep counting forward in eights. Five eights are 40, six eights are 48, seven eights are 56, and eight eights are 64. There are eight eights in 64. If we put the number 64 into the robot and he divides it by eight, the result will be eight because 64 divided by eight equals eight.

40 divided by eight equals five and 64 divided by eight equals eight. We found the results using arrays and our knowledge of the eight times table.

Jacob says that 32 divided by eight is four, and David says that 32 divided by eight is five. Who is right?

This question is all about dividing by eight. Jacob thinks that 32 divided by eight is four, and David thinks that 32 divided by eight is five. Who is correct? To help us work out the correct answer to 32 divided by eight, we could use our knowledge of the eight times table. One times eight is eight, two times eight is 16, three times eight is 24, and four times eight is 32. So, who is correct? It’s Jacob. If four times eight is 32, that means that there are four eights in 32. 32 divided by eight is four. So, Jacob is right. 32 divided by eight equals four.

We used our knowledge of the eight times table to help us divide by eight.

What have we learned in this video? We have learned how to divide by eight using arrays. We also learned how to use the eight times table to divide by eight.

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