Video: Multiplication with Arrays

In this video, we will learn how to write multiplication sentences as arrays with at most 5 rows or columns and investigate how arrays can describe two different multiplication sentences.

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Video Transcript

Multiplication with Arrays

In this video, we will learn how to write multiplication arrays as multiplication sentences. These tins or cans of tomatoes are arranged in rows. How many tins are there altogether? Let’s count how many tins of tomatoes there are in the first row. One, two, three, four, five, six, seven, eight, nine, 10.

The second row also contains 10 cans of tomatoes. How could we write this as a multiplication sentence? We know we have two rows of 10. This is the same as saying two multiplied by 10 or two times 10. We have two rows or two groups. And there are 10 cans of tomatoes in each group. What is two times 10? We need to use our knowledge of the 10 times table. One times 10 is 10, and two times 10 is 20. So the multiplication sentence which matches our array is two times 10 equals 20.

But is there another way we could write this array as a multiplication sentence? We could put the tomatoes into groups of two. This time, we have 10 groups of two. How would we write this as a multiplication sentence? 10 times two. Let’s use our knowledge of the two times table. One two is two. Two twos are four. Three twos are six. Four twos are eight. Five twos are 10. Six twos are 12. Seven twos are 14. Eight twos are 16. Nine twos are 18. And 10 times two is 20.

It doesn’t matter how we arrange the cans of tomatoes. If we arrange them in two rows of 10, there are 20 cans. And if we arrange them in 10 groups of two, there are still 20 cans. The two multiplication sentences we could write for this array are 10 times two equals 20 and two times 10 equals 20. Let’s try some questions now to help us practice writing multiplication arrays as multiplication sentences.

Use the array to find the missing number. Six multiplied by what equals 18.

In this question, we’re shown a multiplication array. And we’re given a multiplication sentence to match the array. But one of the numbers in the sentence is missing. Six multiplied by what equals 18. Where does the number six come from in this multiplication sentence?

Let’s count the number of rows. This array has one, two, three, four, five, six rows. So this is where the number six comes from in the multiplication sentence. How many squares are there in each row? There are three. Six rows of three is 18. Six multiplied by three equals 18. The missing number is three.

Complete the following. Three groups of seven apples is equal to seven groups of what apples.

In this question, we’re shown an array of apples. This array shows three groups of seven apples. We’re asked to find the other multiplication sentence which could be used to describe the multiplication array.

If we make seven groups of apples, how many apples will there be in each group? Let’s make seven groups to find out. We’ve made seven groups. How many apples are in each group? There are three. So the missing number is three. Three groups of seven apples is equal to seven groups of three apples. The missing number is three.

Complete the equation using the given image. Four times five is equal to what times four.

In this question, we’re given a multiplication array. And we’re being asked to think about the two multiplication sentences which match this multiplication array. We’re told the first multiplication sentence is four times five. And this multiplication array shows four groups of five teddy bears. Four rows of five is the same as saying four multiplied by five or four times five.

And we’re told that the second multiplication sentence is a number of groups of four. How many groups of four can we make? There are five groups of four. Four times five is equal to five times four, so the missing number is five.

Pick the array that shows two times nine.

In this question, we’re shown a number of different multiplication arrays, and we have to pick the one that shows two times nine. The first array has two groups, but they’re not equal. The first row has nine counters, and the second row has two. So this is not the correct array.

The second array has two equal groups. How many counters are there in each row? Let’s count. One, two, three, four, five, six, seven, eight, nine, 10. So this array shows two times 10, two groups of 10. This array has two rows of how many counters? One, two, three, four, five, six, seven, eight, nine, two rows of nine, two times nine. This is the array that we’re looking for. The last array shows two times eight or two rows of eight. So this is the array that shows two times nine.

What have we learned in this video? We’ve learned how to write multiplication sentences to match multiplication arrays. And we’ve also learned that we can change the order of the numbers in a multiplication sentence, but the amount stays the same.

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