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.

So welcome to today's lesson, which is called understanding subtraction as decreasing an amount, and it comes from the unit additive structures, addition and subtraction.

Okay, in today's lesson, we will be learning how to describe and interpret subtraction stories, which involve decreasing an amount, and we'll learn to write equations to represent this.

So by the end of today's lesson, you should feel much more confident with writing those equations and representing those stories.

So let's get started.

So our keywords for today are first.

My turn, first, your turn.

And then.

My turn, then, your turn.

And now.

My turn, now, your turn.

And decrease.

My turn, decrease, your turn.

Well done.

So in the first part of today's lesson, we will describe subtraction using first, then, now stories.

And in our lesson today, you will meet Aisha and also Alex.

They're going to be helping us with our learning.

We'll see them throughout our lesson today.

So Alex and Aisha are acting out some first, then, now stories.

This story is different from the addition stories you may have acted out before.

Act out the story with your friends and explain what is different.

First, there are five children standing on the mat.

And what happens here? Then two children leave the mat.

Okay, and now what happens? Now there are three children standing on the mat.

How is this story different from an addition story? That's right.

The amount of children did not increase.

Tell the story again.

First, there are five children standing on the mat.

Then two children left the mat.

Now there are three children standing on the mat.

At the end of the story, what is different from the start of the story? What has changed? That's right, two children were taken away from the whole group, weren't they? The number of children decreased when some children left the mat.

Now, collect some pencils and act out this story.

First, there were six pencils in the pot.

Then two pencils were taken out of the pot.

Now, there are four pencils in the pot.

How many pencils were there at the start of the story? First, there were six pencils in the pot.

That's right.

How many pencils were there at the end of the story? That's right.

Now there are four pencils.

At the end of the story, what is different from the start of the story then? What has changed? That's right, two pencils were taken out of the pot.

The number of pencils decreased when some pencils were taken away from the pot.

Let's check your understanding of that then.

So use the stem sentences to tell this story, okay? And the pictures are there to help you.

So pause the video now while you try that.

And let's see how we got on.

So we can have a look at the picture and say, first, there were four children standing on the mat, then two children left the mat.

Now there are two children standing on the mat.

Well done if you said that.

Explain how many children there were at the start and end of the story.

So this is a check again.

So you need to pause the video now while you explain that.

Okay.

And let's see how we got on with that.

First, that's right, there were four children standing on the mat.

Now at the end of the story, there are two children standing on the mat.

Okay, so what changed between the start and end of the story? Have a think about that.

Pause your video.

Okay, so what changed? That's right, two children left the mat.

The number of children decreased when some children were taken away from the mat.

Okay, so now let's use the stem sentences and the pictures to tell this story.

Okay, so first, there were seven children on the bus.

Then two children left the bus.

Now there are five children on the bus.

We can use numbers to represent each part of this story.

Okay, what number do we think would be at the start there? That's right.

Seven.

The seven represents the number of children on the bus at the start of the story.

Two children have been taken away.

So we need to write a two, don't we? The two represents the number of children that left the bus.

And then in the last box, that's right, five.

The five represents the number of children on the bus at the end of the story.

Okay, so here's some different stories.

Let's tell each story and say how many have been taken away each time.

So here we have, first, there are seven apples on a plate.

Then how many apples were taken away? That's right, three apples have been taken away from the plate.

Now there are four apples on the plate.

Okay, and then let's look at the birds and tell the story.

First, there were three birds on a branch.

Then, that's right, one bird has been taken away from the branch.

It jumped off.

Now there are two birds on the branch.

Okay, and then let's look at the cakes here.

So first, there were five cakes on the tray.

Then, that's right, two cakes have been taken away from the tray, haven't they? So then two cakes were taken off the tray.

Now there are three cakes on the tray.

Well done.

So now time to check your understanding again.

So match each picture to show how many have been taken away.

Okay, so look carefully there and pause the video while you select the correct option.

Okay, how did you get on? So if we look at the story there, we can see first, there are seven apples on the plate.

Then this time, four apples have been taken away from the whole group, haven't they? So now let's look at the next picture.

Okay, so tell the story to yourself and then decide how many have been taken away.

Pause the video while you do that.

And so how did you get on? How many were taken away this time? That's right, it was three have been taken away from the whole group there.

Well done.

Okay, and then let's look at the final picture of the cakes.

Pause the video while you decide how many have been taken away And did you spot it? So this time we can see that one has been taken away from the whole group.

You can see one left at the then part of the story.

So well done if you spotted those.

So now tell the story and fill in the missing numbers.

So let's have a look at the picture to help us.

First, there were four birds on the branch and we write a number four to represent that, don't we? Then one bird left the branch.

One bird has been subtracted.

Now there are? That's right, three birds on the branch.

We can represent this as a subtraction equation.

We can say four minus one is equal to three.

When we subtract from the first part of the story, we decrease the whole amount, don't we? So the whole amount becomes less.

The minus sign shows that some birds have left.

It shows that the amount at the start of the story has decreased.

What does each part of the equation represent? That's right, the four represents the number of birds on the branch at the start of the story.

The one represents the number of birds that were taken from the branch, and the three represents the number of birds on the branch at the end of the story.

The minus sign shows that some birds have been taken away or subtracted.

We have decreased the whole amount at the start of the story.

So now time to check your understanding again.

Tell the story, then fill in the missing numbers to complete the equation.

Okay, so look at the pictures to help you.

Pause the video now.

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

So first, there were? That's right, seven balls in the box.

Then three balls were taken out of the box.

Now there are four balls in the box.

That's right.

Each part of the equation represents? So pause the video now while you do that.

Okay, so let's think.

The seven represents the number of balls in the box at the start of the story.

The three represents the number of balls that were taken from the box, and the four represents the number of balls at the end of the story, doesn't it? Well done.

The minus sign shows that some balls have been subtracted or taken away.

We have decreased the whole amount at the start of the story.

Okay, so let's use the pictures to tell this story now.

So first, there were three cakes on the plate.

Then I took three cakes from the plate.

Now there are no cakes, zero cakes on the plate.

What is different about this story? That's right, there were no cakes left at the end of the story, were they? They'd all been eaten.

Fill in the missing numbers to complete the equation.

So mhm minus mhm is equal to mhm.

Let's do that.

It will be three minus three is equal to zero.

That's right.

What does each number represent? The three represents the number of cakes on the plate at the start of the story, doesn't it? The second three represents the number of cakes that were subtracted from the plate.

They were eaten or taken away.

And the zero represents the number of cakes on the plate at the end of the story, doesn't it? The minus sign shows that some cakes have been taken away.

We have subtracted from the amount at the start of the story and it has decreased.

What did you notice about the amount at the start of the story and the part that was subtracted? That's right.

The amount subtracted was equal to the whole amount at the start of the story.

So the part remaining was zero.

Excellent.

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

So in which of these stories is the whole amount equal to the part that was subtracted? So you can't see the whole amount at the start of the story, but you have to use the pictures to work that out, okay? And think about how you know you're right and explain that.

So pause the video now while you have a try at that.

And let's see how we got on.

Okay, so which one did you choose? That's right.

So we know that when the part subtracted is the same as the whole amount at the start of the story, the part remaining is zero.

So we can see that that has zero at the end of the story.

So the part at the start of the story and the part subtracted must have been equal; they must have been the same.

And you can see in the other two pictures that isn't the case, is it? So well done if you spotted that.

So now let's use the stem sentences to tell this story, okay? And we'll use the pictures as well.

First, there were three LEGO bricks in my tower.

Remember, the then part of the story tells us how many were subtracted, doesn't it? Then I took no LEGO bricks from my tower.

Now there are three LEGO bricks in my tower still, aren't there? What is different about this story? That's right.

There were no bricks subtracted.

So the amount at the start of the story does not decrease.

All parts of the story look the same.

When we subtract zero, the amount at the start of the story does not decrease.

It stays the same, remains the same.

Let's fill in the missing numbers to complete that equation.

Okay, so we will say three minus zero, that's right, is equal to three.

What does each number represent? The three at the start represents the number of bricks at the start of the story, doesn't it? The zero represents the number of bricks that were taken from the tower, and the three represents the number of bricks on the tower at the end of the story.

The minus sign shows that some bricks have been subtracted, but in this case, it was zero.

So nothing changed, did it? It all looked the same, each part of the story.

When we subtract zero, the amount at the start of the story does not decrease, it remains the same.

Okay, so let's check your understanding of that.

Which of these stories shows that zero has been subtracted? Okay, and remember to explain how you know that you're right.

So pause the video now while you try that.

Okay, and let's see which one you selected.

That's right, you can see that all parts of the story look the same there, don't they? When zero is subtracted from the start of the story, the amount does not decrease.

So all parts of the story look the same.

Well done.

We can use counters to represent our story on a first, then, now board.

Let's try together.

Look at each part of the story and think about how many counters we will need.

So first, there are four cats on the cushion.

So we need four counters.

Then two cats left the cushion.

Okay, so you need to take two counters from your four counters in the then part of the story.

Now there are two cats on the cushion.

So you need two counters there, don't you? And then let's write the equation.

How many cats were there at the start of the story? That's right, there were four.

How did the number of cats change? So two cats left the cushion.

So we have to write minus two.

How many cats were at the end of the story.

That's right, there were two cats.

So our equation is four minus two is equal to two.

You can write it in the boxes there, can't you? Let's use counters to represent this story.

First, there were nine drinks on a tray.

Okay, there's our nine drinks.

Then four drinks were taken from the tray.

So we can see four drinks have been taken away, they've been subtracted.

Now there are five drinks on the tray.

So our equation is nine minus four is equal to five.

So your task for the first part of today's lesson is here.

Use a first, then, now card and 10 counters.

Aisha's telling us what to do.

I will listen to the stories read to me and represent them with my counters.

Then I will complete the equations on the first, then, now card.

Remember to retell the story saying what each part represents.

Try to make up a first, then, now story of your own.

Can you tell a story where the amount does not decrease, I wonder? So pause the video now while you try that.

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

You may have done this.

First, there were nine children on the bench.

Then, six children left the bench, so nine minus six.

Now there are three children on the bench.

So it's nine minus six is equal to three, and there are lots of other options you could have chosen as well.

I've just given you one example.

So well done.

You've worked really hard in the first part of today's lesson.

Excellent.

So in the second part of our lesson, we are going to link first, then, now stories to equations, okay? Okay, so let's write an equation to represent this story.

We must remember to tell the story to help us, okay? So first, there were 10 drinks on the tray.

We write 10 to represent that.

This represents the 10 drinks at the start of the story.

Then six drinks were taken from the tray.

So we write minus six.

The six represents the six drinks that were taken away.

We must use the minus sign to show that the number of drinks was decreased.

Now there are four drinks on the tray.

So we write 10 minus six is equal to four.

This represents the four drinks at the end of the story.

Let's check your understanding of that.

Write an equation to represent this story and remember, tell the story to help you.

Okay, pause the video while you try that.

Let's see how you got on.

First, there were five balls in the box.

So you'd write a five, then two balls were taken from the box.

So you write minus two.

Now there are three balls in the box.

Five minus two is equal to three.

Well done.

Aisha and Alex both write an equation to represent this story.

Who is right? Okay, so Aisha says, "I think it is seven minus three is equal to four." And Alex says, "I think it is four minus three is equal to seven." First, there were seven cakes.

So seven must be written first in the equation.

And there we have it.

Seven.

The minus sign represents that some cakes have been subtracted.

It shows we have decreased the amount at the start of the story.

So you'd write seven.

How many were subtracted? That's right, seven minus three.

We can see that three cakes were taken from the plate.

Three were subtracted.

So three must come after the minus sign.

And then we can see seven minus three is equal to four because there were four cakes at the end of the story.

And there's Aisha saying she was right.

Alex didn't put the seven at the start of his equation, did he? So now let's check your understanding again.

Which equation would represent this first, then, now story? Okay, pause the video while you decide.

Remember to tell the story to help you.

Okay, so let's see how we got on.

So let's tell the story.

First, there were eight cats on on the mat, we could say, couldn't we? Then two cats left the mat.

Now there are six cats on the mat.

So we need to have eight at the start of our story, don't we? And there're two cats left, so we have to have minus two.

Okay, so eight minus two is equal to six.

That was the correct equation.

Well done.

Okay, so Aisha writes an equation to represent the story shown.

What is her mistake? So she says, "I think it is three minus six is equal to nine." So what's the mistake that's been made? That's right, you must subtract from the whole amount at the start of the story.

There were nine balls at the start of the story, so that is the amount to be decreased.

So there should have been nine at the start of the equation, shouldn't there? Nine minus, that's right, six is equal to three.

Well done if you spotted that.

So now let's check your understanding again.

Which equation represents this story? Remember, tell the story to help you.

Okay, pause the video now while you decide.

Okay, and what did you think? That's right, it is seven minus three is equal to four.

Well done if you spotted that.

Okay, so Alex writes an equation to represent a story.

Let's think about which story his equation represents.

Okay, he says, "My story can be represented as five minus four is equal to one." Okay? So the first number in the equation is five.

So this represents the number at the start of the story.

And both of the pictures show that there's five at the start, don't they? Four is the second number in the equation.

It represents the amount to be subtracted.

So which picture shows that four were subtracted? That's right.

So five minus four is equal to one.

It's going to be that bottom picture, isn't it? So well done.

Now we'll check your understanding again.

Which story would represent the equation six minus four is equal to two? And explain how you know.

So pause the video again and have a try at that.

Okay, so what did we think? Let's have a look.

That's right, we can see, can't we? That the first number in the equation is six.

So this represents the number at the start of the story.

And they've both got a six.

Four is the number after the minus sign.

It represents the amount to be subtracted.

And we can see that only this second one has four subtracted.

So six minus four is equal to two is represented by that picture.

Well done if you spotted that.

So we can draw counters to represent first, then, now equations.

So draw a first, then, now story for this equation and then tell your story to a partner.

So let's do that together.

The equation is 10 minus four is equal to six, and Alex is drawing the counters here.

So the 10 represents the amount at the start of the story.

So he drew 10 counters.

The minus sign tells us we are decreasing the amount and we can see that the four represents the amount to be subtracted.

So he subtracted four from his 10 there, didn't he in the then part of the story.

And then the six represents the amount that remains at the end of the story.

So Alex drew six counters.

So your task for the first part of the lesson is here, the first part of your task.

Draw a ring around the correct equation to represent each story.

Now, you'll have a sheet with these on, but I'll show you them one at a time.

So there's the first story.

Tell the story and decide which equation represents that.

And then there's another story there to do the same and another story.

So pause the video now while you work through that.

Okay? And then the second part of your task is here.

We can draw counters to represent first, then, now stories.

So draw a first, then, now story for each equation.

Then tell your story to a partner, okay? And remember, you can use counters to help you and then draw them afterwards if you want to, can't you? Okay, so pause the video now while you do that.

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

So here we are, we've got a picture here, haven't we? And we've got to draw a ring around the correct equation to represent each story.

So which equation do you think is correct? That's right.

We know there were seven at the start of the story and three were subtracted and there were four left.

So seven minus three is equal to four.

Then the next story here.

We've got six at the start of the story and we can see that this time, two were subtracted.

So it will be six minus two is equal to four, won't it? There are four remaining.

Okay, and then in our final picture here, we can see that first, there were four balls.

Then one ball was subtracted.

Now there are three balls, so it must be four minus one is equal to three.

So well done if you spotted that.

Okay, so let's have a look at the second part of your task, and you may have done this.

Okay, so we can see that Alex is saying, "I used counters to represent the equation, Then drew the counters." So five minus three is equal to two.

So we've got five counters and then we subtracted three counters to leave two counters.

And then Alex drew the counters, didn't he? Like that.

Okay? And then the second part of our task, five minus two is equal to three.

So there were five counters.

Then he subtracted two counters to leave three counters.

And Alex again drew the counters like that.

So well done if you did that.

Okay, so well done, you've worked really hard in today's lesson and you've learned lots of new information about how to write equations to represent first, then, now subtraction stories.

Excellent.

So let's see what we've learned in today's lesson.

Decreasing the amount in a story is a type of subtraction.

It can be represented as a first, then, now story.

It can also be represented as an equation.

The first amount in a first, then, now story must be written first in an equation because this is the amount to be decreased.

Excellent.

So well done.

I'm hoping you are feeling much more confident now with writing equations to represent those stories and telling and representing those stories yourself as well.

Well done.

You've worked really hard.