Lesson Video: Subtraction Equations Mathematics • Kindergarten

In this video, we will learn how to read, write, and model subtraction equations with numbers up to 10.

13:12

Video Transcript

Subtraction Equations

In this video, we’re going to learn how to read, write, and model subtraction equations with numbers up to 10.

Here’s a group of balloons. It contains one, two, three, four, five, six balloons. Now, let’s imagine a hedgehog comes along. But the prickles on a hedgehog and our six balloons don’t mix very well. What if the hedgehog pops two of the balloons? One, two. Now, how many balloons are left? We know that the number of balloons that are left will be the same as six take away two. They’re going to be one, two, three, four balloons left.

We’ve subtracted or taken away two from six to give the answer four. Six take away two equals four. But, you know six take way two always leaves four. If there are six birds and two of them fly away, we’re left with four birds. It doesn’t matter if we model a subtraction using six counters or six cubes; when we subtract two from six, the answer is always four.

Now, what if there was a way for us to show that six take away two equals four without us having to draw balloons or use counters. Wouldn’t that be useful? Well, we can do this. And we do this by writing what’s called an equation. And because we’re thinking about taking away and subtracting, this is going to be a subtraction equation. Now, the word equation might sound tricky, but all it means is a way to show a number fact using numbers and symbols. In other words, we’re going to show that six take away two equals four without drawing any pictures, without writing any words, just using numbers and symbols.

The first thing that we can do is to show that number that we start with. This is the number that we had before we took anything away. And in this number fact, it’s the number six. So, we’ll write the digit six. Now, we need a symbol to show that we need to take away two. And we can use the subtraction symbol. The subtraction symbol is a horizontal line that looks like this. This symbol means take away or subtract. And, of course, we know we’re taking away two, so we can write the digit two after this symbol.

Next, we need a symbol that represents “is equal to” or “is the same as.” Six take away two is the same as four. So, we can use the equal sign. We draw two lines. And the final part of our equation is the number that we have left, which is four. Six take away two is equal to four. You know, we can show any subtraction fact we want using an equation like this. Let’s practice answering some questions where we have to think about subtraction equations.

Which picture shows five take away four equals one?

In this question, we’re given a subtraction equation or a number sentence. An equation or a number sentence is a way of showing a number fact using numbers and symbols. In this particular number sentence, we can see the number five then this symbol that looks like a short line. This is the symbol for taking away or subtracting. Then, we have the number four. This is the number that we need to take away.

Then, we can see the equal symbol. And after that comes the answer. This is the amount that we have left. We can read this number sentence as five take away four equals one. So, which picture shows five take away four equals one? And as we’ve said already, the number five represents the number that we’re starting with. Let’s go through each of our pictures to see which one contains five objects to begin with.

Our first picture shows one, two, three doughnuts. This picture doesn’t start with five, does it? Let’s look at the group of dogs. We have one, two, three, four, five dogs. This picture could show five take away four equals one. In our second set of doughnuts, there are one, two, three, four, five. This could be the correct one. Then, we have a group of one, two, three, four sweets. This is too small. And our final picture shows one, two, three, four, five sweets. So, the picture that we’re looking for is either the row of dogs, the longer row of doughnuts, or the longer row of sweets because they all contain five objects to start with.

The second number in our subtraction equation is the number four. And this shows us the number that we need to take away. In these pictures, we can see the objects that have been taken away because they’ve been crossed through. How many dogs have been taken away? One, two. The picture of the dogs shows the subtraction five take away two. What about the long row of doughnuts? We’ve taken away one, two, three, four. This shows the subtraction five take away four. This is the subtraction we’re looking for. Looks like this is going to be our answer. Let’s just check the row of sweets.

Well, if we look, we can see that only one sweet has been crossed out. This shows the subtraction five take away one. The last number in our number sentence is one. Five take away four equals one. And we can see in our row of doughnuts that this is true. Five doughnuts take away four doughnuts leaves us with one doughnut. The picture that shows five take away four equals one is the row of doughnuts that shows five doughnuts with four of them crossed out and one left over.

Yesterday, Alice had four sweets. She ate two. How many are left? Find the matching number sentence. Two plus one equals three, four take away three equals one, two plus two equals four, four take away two equals two, or four take away one equals three.

Our problem starts by telling us that yesterday Alice had four sweets. But she doesn’t have four anymore. She ate two of them. And we can see this in the picture, can’t we? There’s a row of four sweets and two of them have been crossed out. These are the two that Alice has eaten. Our first question asks us, how many are left? Let’s count the sweets that haven’t been eaten. There are one, two sweets left. So, Alice started off with four sweets, she ate two of them, and she’s got two left.

In the second part of our problem, we’re asked to find a matching number sentence. A number sentence or an equation is a way to show a number fact using numbers and symbols. The first thing we can do here is to think about what sort of number fact are we looking for. We know that Alice started off with four sweets and then she ate two of them. Another way of thinking of this is that she’s taken away two of them.

The answer’s going to be less than the number she started with because she’s eaten them. So, we’re looking for a number sentence that shows a subtraction fact or a take away fact. And the symbol that represents subtract or take away is a little line like this. We can see this symbol in three of our possible number sentences. The others show an addition symbol. But this isn’t an addition fact. Alice isn’t adding her sweets, so let’s cross through the addition number sentences. We’re looking for a subtraction number sentence.

Alice starts off with four sweets, she eats two sweets, and she has two sweets left. Which number sentence shows four take away two? It’s this one here. We started off by finding that Alice has two sweets left. And the matching number sentence is four take away two equals two.

There were three cats on a roof. Two of them jumped down. There was one cat left on the roof. Fill in the blank. Three take away what equals one?

In this question, we’re given a number story. But as well as that, we’re given a number sentence or equation with a missing number in it. And the two things go together. To start with, let’s think about the story. Our story begins with three cats on a roof. Here are three counters to represent our three cats. In the next part of our story, we’re told that two of the cats jumped down. Suppose we could represent this with our counters by taking away two of our counters cause the cats aren’t on the roof anymore. One, two.

The final part of our story tells us there was one cat left on the roof. This is shown in our model because we have one counter left. We had three, we took away two, and now we’ve got one.

Now, let’s look at the number sentence or equation. We’re told to fill in the blank. If we look carefully at this subtraction equation, we can see that it has a missing number in it. Three take away what equals one? In our story, what did we take away from three that left us with one? Well, the number three represented the number of cats that were on the roof or the number of counters that we had in a row to start with. This means that our missing number is the number that we took away from three. This is the number of cats that jumped off the roof.

We know that two cats jumped down. That’s why we subtracted or took away two counters. And the final number in our number sentence is the number that we have left. If we subtract two from three, we’re left with one. The number sentence that matches our story about the cats is three take away two equals one. Our missing number is two.

So, what have we learned in this video? Well, firstly, we’ve learned that a subtraction equation or number sentence is a way to show a subtraction fact using numbers and also symbols. And so, we’ve learned how to read, write, and model subtraction equations with numbers up to 10.

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