Lesson video

Hello, my name's Mrs. Cornwell and I'm going to be helping you with your learning today.

I'm really looking forward to today's lesson.

I know you're going to work really hard and will do really well.

So let's get started.

Welcome to today's lesson, which is called "Find the Missing Part of a Subtraction Story," and it comes from the unit Additive Structures, Addition and Subtraction.

So, in our lesson today, we are going to be finding the missing part in a subtraction story when the other two parts are known.

So we're going to find out what strategies we can use to find those missing parts.

Okay, so let's get started.

So our keywords for today are add.

My turn, add, your turn.

And subtract.

My turn, subtract, your turn.

And then my turn, then your turn.

And first.

My turn, first, your turn.

Well done.

Excellent.

So, in the first part of our lesson today, we're going to solve a subtraction story when the first part of it is missing, okay? So in this lesson you will meet Aisha.

and you will also meet Alex.

They're going to help us with our learning today.

So tell and act out this story with your friends to help you find the missing part.

Okay, so we don't know how many children were on the mat at first, then three children left the mat.

We can see them there.

Now, there are two children on the mat.

Is this an addition or a subtraction story, do you think? And how do you know? That's right, we know it's a subtraction story because the amount at the start of the story decreased, didn't it? And we can see the equation to represent it there.

Mm minus three is equal to two.

We changed the amount at the start of the story by subtracting three children.

So to undo the change, we must add them back on again.

Okay, so we can see there the three children that were subtracted, okay? And so we need to add them back to the amount that was left at the end of the story, and then that will give us the number at the start of the story, the amount at the start.

So it was five minus three is equal to two.

Let's use counters to tell this story.

We don't know how many counters there were at first, then four counters were subtracted.

Now there are two counters on the tens frame.

We can use this to solve the equation.

Mm minus four is equal to two.

We changed the amount at the start by subtracting four counters.

So to undo the change, that's right, we need to add them back on again, don't we? So we know we had two at the end of the story and we need to add that four back onto the two.

So there we go.

If we add them back on, we can see that the number at the start of the story was six.

There were six counters at the start of the story.

So now it's time to check your understanding.

Tell the story and use it to find the missing part and then complete the equation.

So pause a video now while you do that.

Okay, so let's see how you got on with that then.

So we need to tell the story, don't we, to help us? We don't know how many counters were on the tens frame at first, but then three counters were subtracted.

Now, there are six counters left on the tens frame.

So we changed the amount at the start by subtracting three counters.

So that's right.

To undo the change, we needed to add them back on again, didn't we? So we needed to have our six at the end and add three back to that six.

And if you do that, you can see that there were nine counters at the start of the story.

That's right.

Well done if you spotted that.

So, Alex thinks a missing number here is one.

What mistake has been made? So mm minus five is equal to four.

So let's tell the story.

We don't know how many counters there were at first, then five counters were subtracted.

Now there are four counters on the tens frame, okay? So let's think about this.

Alex started with five and subtracted four.

That's what he did.

But it is five at the start of the story? No, you can see that five is the amount that was subtracted.

So let's think about what has changed to help Alex understand.

Five counters were subtracted.

So to undo the change, we must add five counters back on again.

So there we can see if we add five counters to the amount at the end of the story, it will take us back to the amount at the start of the story, won't it? And we can see that it should have been nine minus five is equal to four.

There were nine counters at the start of the story.

So now it's time to check your understanding again.

Match the correct story to the equation, then solve it.

Okay, so we've got mm minus six is equal to one, okay? So pause the video now while you have a think about that.

Let's see how you got on them.

So, if we have a look, the equation is mm minus six is equal to one.

Okay, so which story subtracts six and leaves one at the end of the story? That's right.

It's the second story, isn't it? That one there.

And if we think about how to solve the equation, we change the amount at the start by subtracting six counters.

So to undo the change, we must add six counters back on again.

So if we have a look there, if we add them back on, we can see that at the start of the story, at the start of the story, there were seven counters.

So well done if you did that.

So, here we've got Alex again then.

Alex hides some parts of his story and ask Aisha what amount could be at the start of the story.

So mm subtract four or minus four is equal to mm.

So we can only see the amount subtracted.

Aisha says this story may start with three.

Do you agree? That's right.

This cannot be correct, because the number at the start of the story cannot be less than the amount subtracted.

So you can't have three because you wouldn't have enough counters to subtract four, would you? The number at the start must be four or more.

When we can see the end of the story, we can solve the equation.

So now we can work out exactly how many counters were at the start of the story, can't we? We changed the amount at the start by subtracting four.

So now we must add four back on again.

So we know we had four at the end of the story and we subtracted four.

So we add them back on again.

And now we can see at the start of the story, there were eight counters, weren't there? So well done.

So it's time to check your understanding again now.

Which equation represents this story? So we've got a, mm minus three is equal to four, b, mm minus four is equal to three, and c, mm minus four is equal to seven.

So pause the video now while you think about that.

Okay, and let's see, what did you think? That's right, it was b, mm minus four, because we can see four were subtracted is equal to three, because there are three at the end of the story.

And we can see that there would've been seven at the start of the story, wasn't there? Okay, so here's your task for the first part of today's lesson.

Okay, so you need to work with a partner.

You can see Alex and Aisha are partners there, aren't they? So Alex is telling us, we will each make up a subtraction story with the first part missing and draw it on the storyboard.

Then Aisha tells us, then we will swap our stories and use a tens frame to solve them.

Remember to write the equation to match your story when you've told the story.

Okay, pause your video now while you try that.

Okay, so the second part of your task is to use your counters on a first, then, now board to help you find the missing number in each equation.

Okay, so remember, use what you've learned in today's lesson to help you with that.

And while you are working, I want you to think about what you notice about the missing numbers in each equation.

Okay, so do you spot a pattern? You're going to be a pattern spotter today, aren't you? So have a think about that and see if you can explain why that pattern happens.

Okay, so pause the video now while you try that.

Okay, so let's see how you got on with that then.

So you may have done this.

Alex is telling us what he did.

So he says, "I started with seven, then subtracted three.

I hid the number at the start from my partner." So he started with seven and he subtracted three, but then he hid it.

And then Aisha, she worked out how many he had at the start because she says, "I knew three had been subtracted, so I added three back to the four counters at the end of the story." So when she added those back on, she could see that the start of the story, at the start, there must have been seven counters.

So, well done if you did that.

Okay, so let's see how you got on in the second part of our task then.

So you had to find the missing numbers in the equations, didn't you? And use your counters on a first, then, now board to help you with that, okay? So let's have a look at this first one, a, so something minus one is equal to five, okay? So if we subtracted one from the number at the start of the story and it left five, we need to add that one back onto five to find out what that number we started with was.

Okay, so let's have a little look.

So, we know that if we add one back onto five, it would be six.

So six minus one is equal to five.

Well done.

And then you would use the same strategy to find out that seven minus two was equal to five, eight minus three was equal to five, and nine minus four is equal to five.

Okay, so well done.

And did you spot a pattern in our equations there? That's right.

In each equation, the difference, the five at the end remained the same.

So when each subtrahend increases by one, the minuend must also increase by one.

So well done if you spotted that.

Okay, so now we're going to move on to the second part of our lesson where we're going to solve a subtraction story when the then part is missing.

Okay, so here's Alex again, and he says, "This time, I have hidden a different part of my story," and Aisha's saying, "How would we represent this as an equation?" So we can see that we've got five at the start of the story, and then we don't know how many were subtracted, but there were three at the end of the story.

So it would be five minus mm is equal to three.

Let's tell the story to help us solve the problem.

First, there were five cakes on the plate, then some cakes were eaten.

We don't know how many, do we? Now, there are three cakes on the plate.

So how many cakes were eaten? How will we find out? Aisha's saying, "I will use what I already know to help me." So we changed the whole amount at the start by subtracting some cakes, didn't we? Five is the whole, and we know three is the part that is left.

So the part subtracted must be two.

And there we go.

Five minus two is equal to three.

Let's use a picture to tell a new story.

And we can see there's an equation at the bottom.

Six minus mm is equal to two.

First, there were six counters on the tens frame, then we don't know what happened.

Now, there are two counters on the tens frame.

We can use the story to solve the equation, can't we? We changed the whole amount at the start by subtracting some counters.

Six is the whole and two is a part.

The part subtracted must be four.

That's right, when six is the whole and two is a part, the other part is four, and we can see four was subtracted.

Okay, so now it's time to check your understanding again.

So tell a story and use it to find the missing part, okay? And then complete the equation.

So use those pictures there to help you tell that story.

All right, pause the video now while you try that.

Okay, and let's see how you got on then.

So, the story, first, there were nine counters on the tens frame.

We don't know what happened then.

We know some were subtracted, but we don't know how many.

Now, there are six counters on the tens frame.

So we changed the whole amount at the start by subtracting some counters.

Nine is the whole and six is a part.

So the part subtracted must be three.

That's right, nine minus three is equal to six.

Well done.

Okay, so now we've got another problem here.

Who is right? Explain how you know.

So we've got Aisha and she's looking at that story, those pictures, and she's saying, "I think the missing number is three." And we've got Alex and he's looking at the same story, and he's saying, "I think the missing number is five." So who do you think's right? So we changed the whole amount at the start by subtracting some counters.

Four is the whole and one is a part.

So what do we think the other part, the part subtracted will be? That's right, the part subtracted must be three.

So well done if you noticed that.

And there it is in the equation.

Okay, so now it's time to check your understanding again.

Tick which story matches the equation, then solve it.

So the equation is six minus mm is equal to four.

We're trying to find out how many were subtracted.

So look carefully at the stories, okay? And pause the video now while you have a try at that.

Okay, and let's see how you got on.

So we can see that six is the whole amount, the minuend there, isn't it, at the start of the story? And both stories start with six.

We don't know the subtrahend, the amount subtracted, but the remaining part was four.

So we can see that that first story had four as the remaining part.

So that must have been the correct choice.

Well done.

Now, we changed the whole at the start by subtracting some counters, didn't we? Six is the whole and four is a part.

It's the remaining part.

So the part subtracted must be two.

That's right.

Well done.

Excellent.

And there you can see the two counters subtracted there.

Aisha and Alex are playing Guess My Number.

Aisha only shows some of her story and she hides the then part of her story.

Alex says, "I think you may have subtracted seven." "That cannot be true here," Aisha says.

How do we know that Aisha's right? That's right, the amount of counters subtracted cannot be greater than the amount at the start of the story, can it? If you've only got four counters at the start, then you can't subtract more than four counters because you wouldn't have enough, would you? So now it's time to check your understanding again.

Use your counters to help Alex find what the missing part could be, okay? So pause the video now while you try that.

Okay, and let's see how you got on.

So, we can see that he had four counters at the start of the story.

He tells us, "I only have four counters, so I cannot subtract more than four counters." So it could be four that he could have subtracted, or it could have been three, couldn't it? Or it could have been two, or it could have been one, or it could have been zero, but it couldn't have been an amount more than four, could it? So well done if you noticed that.

Okay, so here's the task for the second part of today's lesson.

Work with a partner.

Here's Alex and Aisha again.

And Alex is saying, "We will each make up a subtraction story with the then part missing and draw it on the storyboard." And Aisha says, "Then we will swap our stories and use a tens frame to solve them." Remember to write the missing number equation to match your story.

Okay, so pause the video now while you try that.

Okay, and then here's the second part of your task.

Use your counters on a first, then, now board to help you find the missing number in each equation.

Think about what you notice, so you're going to be pattern spotters again, what you notice about the missing number in each equation and explain why that pattern happens.

So pause a video now while you try that.

Okay, so let's see how you got on with your task today.

You may have done this.

So Alex is saying, "I started with seven, then subtracted two.

I hid the number I had subtracted from my partner." So there's his seven, then he subtracted two, and he hid it, okay? Then Aisha's saying, "There were five counters remaining at the end of the story.

Seven is the whole, and five is a part, so the subtracted part must be two." That's right.

Okay, seven minus two is equal to five.

Well done if you did that.

Okay, now the second part of your task was to use your counters on a first, then, now board to help you find the missing number in each equation.

Okay, so let's have a look.

So for a, you'll put nine counters on, and then you think nine is the whole, and five is the remaining part.

So the missing part must be four.

That's right.

And then we would have eight minus three is equal to five.

Seven minus two is equal to five, and six minus one is equal to five.

And you may have noticed the pattern.

Each equation ends with the same difference, doesn't it? They all end with five.

So if there is one more at the start of the story, one more must also be subtracted.

Yeah, well done.

Excellent if you spotted that.

You've worked really hard in today's lesson, haven't you? So let's think about what we've learned today then.

When we change an amount by subtracting, to undo the change, we must add the same amount back on again.

To find the amount subtracted, we can use the whole amount at the end of the story and the part we can see to find the missing part.

So well done.

You've worked really hard there today, haven't you? And I've really enjoyed working with you.

Excellent.