Lesson video

Hello, everyone.

Welcome back to another maths lesson with me, Mrs. Pochciol.

As always, I can't wait to learn lots of new things, and most importantly, have lots of fun.

So let's get started.

Today's lesson is called "Using Known Addition and Subtraction Facts," and it comes from the unit "Solving Problems in a Range of Contexts." By the end of this lesson, you will be able to use known addition and subtraction facts within 10 to help you to solve problems. Let's have a look at this lesson's keywords: represent, calculate, efficient, and strategy.

Let's practise them.

My turn.

Represent.

Your turn.

My turn.

Calculate.

Your turn.

My turn.

Efficient.

Your turn.

My turn.

Strategy.

Your turn.

Fantastic.

Now we can say them, let's use them.

Let's have a look at our lesson outline.

In the first part of our learning, we're going to be visualising and representing problems. And in the second part of our learning, we're going to be calculating using the most efficient strategy.

Are we ready? Let's get started with visualising and representing those problems. In this lesson, you are going to meet all of our Oak children: Izzy, Laura, Lucas, Sofia, Aisha, Sam, Andeep, Jacob, Alex, and Jun.

How lucky we are to have all of these children joining us today.

The children continue with their afternoon in their classroom.

They continue their job of being maths detectives.

Have a look at this picture.

What mathematical stories do you think you could see? Hmm.

Lots of different things happening here.

Let's see what the children find.

Andeep and Sam both look at the robots to see if they can create a mathematical story with them.

Hmm.

What do you think that they can see here? Let's have a look Andeep's first.

Andeep, what mathematical story can you see with the robots? "There are five robots on the table.

Two robots are lying down.

How many robots are standing?" Oh, I love that problem.

Well done, Andeep.

I can see that you've spotted that some of them are standing up and some of them are lying down.

Let's see.

Sam, what did you see? Oh.

Sam says, "There are three robots standing.

There are two robots lying down.

How many robots are there all together?" Wow! You've both created your own problems to represent the same picture, but they sound different.

Shall we have a look at the maths behind their stories? Both of the children represent their stories and show them as an equation.

So let's have a look.

What maths can we see? Andeep notices that his story was a subtraction because he's subtracting apart from the whole.

So he will represent this using his bar model.

Five robots, two of them are lying down.

How many of them are standing? So five subtract two.

Sam notices that her problem is an addition.

Wow, a subtraction and an addition from one picture.

Well done, guys.

Sam is combining two different parts.

She's combining the robots that are standing up with the robots that are lying down.

So her bar model will look like this.

Three plus two is equal to something.

I love that you've both been able to represent different stories but from the same picture.

Well, done guys.

We'll be calculating in the next part of our learning, so keep a hold of those bar models and equations and think about how you're going to solve them.

Let's have a look at what Sofia noticed.

Oh, Sofia has zoomed in on the names on the board.

What's your story, Sofia? "First, Mr. Acorn wrote four names of children who had to complete an activity.

Then four of the names were crossed off.

How many children are left to complete their activity?" Wow, I love how you've created that story, Sofia.

So how are you going to represent it? Sofia's going to represent this using a first, then, now model.

First, there were four names on the board.

Then, four names were crossed off.

Hmm.

So how many names are left? We can represent this as four subtract four is equal to something.

Well done, Sofia.

I loved your first, then, now story.

Well done.

Okay then, over to you.

So which of these can be represented using the equation 10 subtract 4 is equal to something? Hmm.

Get your detective hats on.

Let's have a look at our pictures.

Remember, we're looking for a picture that represents 10 subtract 4.

Hmm.

Is it this one? Could it be this one or could it be this one? Pause this video.

Have a think.

Which of those pictures could be represented by 10 subtract 4? I suggest you look really carefully at the items and the objects and also the arrows in this picture.

Welcome back.

I hope you enjoyed being maths detectives there.

Did you manage to find a picture that could be represented by 10 subtract 4? Hmm.

Let's see what Lucas noticed.

Lucas looked for a picture that had a whole of 10.

Yes, because in our equation, we can see that the whole is 10.

And in this picture, Lucas noticed that there were 10 books all together.

Well done of you spotted that it was this picture that could be represented by 10 subtract 4.

Now, the next part of your challenge.

Could you represent this problem using a model, any that you choose, and tell your own mathematical story to explain what is happening in this picture? Remember, it can be represented by 10 subtract 4.

So make sure you keep that in mind while you're creating your story.

Pause this video and come on back once you've represented the problem and come up with your own story.

Welcome back.

I hope you enjoyed getting creative there with your stories.

Should we see what Lucas did? "First, there were 10 books on the bookshelf.

Then, Jacob took four of them.

How many books are on the bookshelf now?" Well done, Lucas.

I can see clearly that you've used the correct numbers there, but let's check with a representation that you have represented it in the correct way.

Lucas is going to use a first, then, now model to represent his story.

First, there were 10 books.

Then, four books were taken.

Let's double check.

Can this be represented by 10 subtract 4? Let's have a look.

First, there were 10.

Then, four were taken.

Well done, Lucas.

This can be represented as 10 subtract 4.

There were 10 books and four were taken.

So we can see that is 10 subtract 4.

Well done.

Don't worry about how many books are left just this minute because we're going to be calculating later on in our learning, but well done For representing this problem.

A big part of maths is making sure that we understand and can represent a problem before we can calculate it.

So you're already halfway there.

Well done.

Some great work there from our Oak children.

So now it's over to you with task A.

Create your own stories using this classroom image, or you might actually like to use your own classroom.

Once you've created a story, can you represent this problem mathematically? Remember, we're not solving our problems just yet.

The first part of our learning is just to visualise and represent these problems. So set up your problem, ready to calculate later.

I would like to see a story, a representation, and an equation to represent your problem.

Once you've created them, you might like to share them with your friends.

Pause this video, have a go at finding some of your own problems and representing them and come on back once you're ready to continue with the learning.

Welcome back.

I hope you enjoyed being maths detectives and I hope you enjoyed sharing all of your problems with your friends.

Did you find someone that did the same problem as you? Did you find someone who did the same situation but looked at it differently? Hmm.

Let's have a look at what John did.

John created a story to represent the building blocks.

Wow.

I wonder what John could see in this problem.

How did you see it, John? "There are five blue blocks.

There are four yellow blocks.

How many blocks are there altogether?" Wow.

I love that problem, John.

Now, how are you going to represent it? John represents his story as a bar model and writes the equation.

There are five blue blocks and four yellow blocks.

So five is a part and four is a part.

In this story, John is finding out how many blocks there are altogether, so it must be an addition.

For John to find the whole, he needs to calculate five plus four.

John also records this as four plus five because he knows that addition is commutative so he can swap the addends around, but the sum will remain the same.

So he could either calculate five plus four or four plus five to find the whole for this problem.

Well done, John.

So let's move on to the second part of our learning.

We've done some great visualising and representing.

Now it's time to calculate, thinking about the most efficient strategy.

Let's get going.

So let's recap Andeep's story before we help him calculate.

Remember, he was looking at those robots and he saw five robots on the table.

Two of those robots were lying down, so he wanted to know how many robots were standing.

Hmm.

He recorded this as five subtract two is equal to something.

Andeep notices that there are a few ways that he could calculate this problem.

Which one are you gonna go for, Andeep? Andeep decides to solve this using his knowledge of odd numbers and adding and subtracting two.

He knows that five is an odd number and two less than an odd number will be the odd number before.

The odd number before five is three.

So five subtract two must be equal to three.

Well done, Andeep.

Let's hear your story now then.

"There were five robots on the table.

Two robots are lying down, and there are three robots standing." Well done, a great story there, Andeep.

Now let's have a look at Sam.

Let's recap Sam's story before we calculate.

Remember, Sam's story was looking at the same picture that Andeep was, the robots.

Let's remind ourselves of the problem.

There were three robots standing.

There were two robots lying down.

And Sam wanted to work out how many robots there were altogether.

She recorded this as three plus two is equal to something.

How are you gonna calculate this then, Sam? Sam knows that three and two combine to make five.

She didn't have to do any calculating at all because she already knew that fact.

I'm very impressed, Sam.

Well done.

Let's retell your story then with this sum.

There are three robots standing.

There are two robots lying down.

There are five robots altogether.

A beautiful story there, Sam.

Well done.

Sam and Andeep now notice that their addition and subtraction calculations are very similar.

Andeep found that five subtract two is equal to three and Sam found that three plus two is equal to five.

What do we notice there? Andeep has noticed that their facts must be related because they have the same wholes and the same parts.

Yes, Sam, five is the whole, three is a part, and two is a part in both of their equations.

We know that we can use addition facts to find subtraction facts and vice versa.

We can use the stem sentence, "If I know hmm, then I know hmm." We've used that stem sentence before.

So actually, only one of them would've needed to solve that problem because then the other one could have used their answer to help them solve theirs.

They both practise using the stem sentences.

If I know three plus two is equal to five, then Andeep would've known that five subtract two is equal to three.

And if Sam knew that five subtract two was equal to three, then she would've known that three plus two was equal to five.

Wonderful! Let's help Sofia now then.

So Sofia's going to calculate her problem.

Sofia, can you remind us of your problem first? "First, Mr. Acorn wrote four names on the board.

Then, he crossed off four of them.

Now, how many names are on the board?" And we recorded this equation as four subtract four is equal to something.

Come on then, Sofia, how are you going to calculate this problem? Sofia notices that she's subtracting a number from its itself.

When we subtract a number from itself, we know that it has a difference of zero.

So we had four and we removed four, which means that there will be none left.

So four subtract four must be equal to zero.

So Sofia, can you recap your story then now that you know the solution? "First, Mr. Acorn wrote four names on the board.

Then, four of them were crossed off.

Now, there are no names on the board." They've all completed their activities.

Well done, everybody.

Right then, over to you.

Let's see if we can help Lucas calculate his story.

Let's remind us of his problem.

"First, there were 10 books on the bookshelf.

Then, Jacob took four of them." Lucas wants to know how many books are left on the shelf now? He recorded this story as 10 subtract 4 is equal to something.

Aisha and Jacob both explain how they would calculate this unknown part.

Jacob decides that he's going to use a number line to solve this.

He starts at 10 and he subtracts four.

He thinks the unknown part is seven.

Aisha knows that six and four combine to make 10, so 10 subtract 4 must be equal to six.

Aisha thinks differently.

Aisha thinks that six is the unknown part.

Hmm.

Whose calculation is correct? Pause this video.

Have a look at Jacob and Aisha's strategies and can you work out who is correct? Is it seven or is it six? Welcome back.

I hope you enjoyed looking at some of the children's strategies there.

So who was correct? Was seven the unknown part or was six Lucas's unknown part? Aisha was correct.

Well done if you said that Aisha was correct.

Oh, Jacob, a really good try there, but it seems like you counted the lines and not the steps in between.

The unknown part should have been six.

Well done, Aisha, and well done to you if you spotted that.

Okay then, over to you for task B.

Just like the children, you're going to solve the problems that you created within task A.

I would really like you to think about the strategy that you're going to find the sum or the difference.

Think about what's going to be the most efficient.

Let's remind ourselves of Jun's problem before he gets on trying to solve it.

There are five blue blocks.

There are four yellow blocks.

And June wants to know how many blocks there are altogether.

So pause this video.

Don't forget to double check your answer when you're finished to make sure that it's correct.

Come on back when you're ready to complete the lesson.

Welcome back.

I hope you enjoyed calculating.

Should we see how Jun's got on? Jun, how are you going to solve your problem? There are five blue blocks and four yellow blocks.

How many blocks are there altogether? Ah, because addition is commutative, we could calculate either five plus four or four plus five as they would both give us the same sum.

But Jun's decided to focus on five plus four.

Come on then, Jun, show us how you did it.

Jun noticed that the addends have a difference of one, so he can solve this using a near double strategy.

Jun knows that double five is 10, but five plus four is one less than 10, which is nine.

So five plus four must be equal to nine.

Well done, Jun.

Can you tell us your finished story then? "There were five blue blocks.

There were four yellow blocks.

There are nine blocks altogether." Well done, Jun, and well done to you for calculating your problems. Shall we have a look at what we've learned today? In order to solve a problem, we must visualise it and represent it.

We can represent a problem in many different ways, including bar models, first, then, now models, and equations.

Once we can see a problem, we know what to calculate.

To calculate a solution, we can use a range of strategies.

We can use our knowledge of addition facts to help us solve subtraction facts and we can use our knowledge of subtraction facts to help us to solve addition facts.

I hope that you continue to be a detective in everything that you see around you.

Thank you for joining me with your learning today.

I hope to see you all again soon.

Goodbye!.