Lesson video

Hello, my name is Mrs Behan.

And for this lesson, I'm going to be your teacher.

In this lesson, we're going to learn how to draw bar models, to help us solve multiplication and division problems. And it's all about putting the known values and the unknown values in the right places.

Let's begin by having a look at the lesson agenda.

We're going to have a look at some bar models and we're going to try and match them to word problems to see how they can help us.

Then I'm going to teach you how to draw the bar model for yourself to solve some problems. We'll then have a practise and then you'll be ready to complete your independent task.

And don't worry, I will make sure I go through the answers with you.

There's just two things you're going to need for this lesson.

Something to write with, so a pencil or a pen, and something to write on.

If you don't have those things to hand, pause the video and now whilst you go and get them.

And remember, try to work somewhere quiet where you aren't going to be disturbed for the lesson.

Take a look at this bar model.

So this bar model helps us to solve one equation.

There are four options coming up on the screen.

Does this bar model help us solve option one? Does this bar model help us solve option two? Does this bar model help us solve option three? Or does the bar model help us solve option four? Think about the values that we know and the unknown values.

Pause the video here whilst you have a look.

Take as long as you need, and when you're ready, come back to me.

By the way, if you do manage to work it out, I would like you to try and convince me how you know.

You might want to practise on somebody else in your house first.

Convince them that the option you chose is the right one.

Okay, off you go.

Okay, so which one did you pick? I'm sure you didn't pick option one.

We don't have 22 as a known value.

We don't know that one, so it can't be that.

Option two, 22 multiply by four.

Once again, we can't see 22 in the bar model, so we don't know it's not going to help us solve that one.

Option three, 88 divided by four.

Well, we can see 88 as a whole, and we can see four parts divided equally.

So I think that's the one that's going to help us.

This bar model doesn't help us solve 88 divided by 22.

So did you have a go at convincing me? If I was to convince somebody, this is what I would say.

The whole is 88.

Can you say that? The whole is 88.

The whole has been divided into four equal parts.

You say it with me.

The whole has been divided into four equal parts.

And we can see that up on the bar model nice and clearly.

There are four equal parts.

And then let the person know the unknown is the size of each part.

So even though I have a question mark here, I could have a question mark here and here and here because there are four parts and I don't know the size of any of them.

So my calculation would be 88 divided by four.

That's what the bar model helps me work out.

So 88 divided by four is equal to 22.

So I can change the value there on my bar model and now it's complete.

So if that is the calculation, I wonder what the number story could be.

Just have a think.

What could the number story be if the calculation is 88 divided by four equals 22? So I hope you got creative and come up with some fun number stories.

Here is my example.

Mrs Behan spent 88 pounds on concert tickets.

She bought four tickets.

How much did each ticket cost? Well, this bar model helps with this word problem, because the whole is 88, and it was shared out between four tickets.

So I need to know the value of each ticket.

So the bar model would help me work out I need to divide by four.

I did another example.

Here's my next story.

Mrs Behan needed new tyres for her car.

She spent 88 pounds for four new tyres.

What was the cost of each tyre? I can tell you that this was very cheap for tyres.

88 pounds was the whole.

88 was the whole and there are four tyres.

So what I needed to work out 88 divided by four to realise that each tyre costs me 22 pounds.

It's a bargain.

And my last number story that I have for you is about going to the restaurant.

Mrs Behan ate at the same restaurant for four days in a row and spent the same amount of money each day.

She spent 88 pounds.

How much did she spend each day? So I know the overall amount that was spent was 88 pounds.

I went over four days and spent the same amount each day.

So I need to do 88 divided by four to realise I spent 22 pounds each day.

That's a lot of money on food.

So next I'm going to show you how to draw your own bar model.

Bar model is the easiest to use when they're lovely and clear and they're are well labelled, just so that we don't get confused.

However, it is important to remember, it is just a model and we don't need to draw things to scale.

It's just a model that will help us work out what the masses that we need to be able to solve the problem.

I know you are a super reader, so let's use your skills to read this word problem.

Okay, let's do it together.

84 policemen were at Silverstone helping cars to enter and park.

An equal number of policemen were placed at each of the four gates.

How many policemen were at each gate? So to draw a bar model, we need to know what the known facts are.

So let's go through.

84 policemen were at Silverstone.

So we know that's the whole number of policemen.

We know that an equal number of policemen were placed at each of the four gates.

So we can start to build a picture in our minds of 84 policemen all being shared between four places with an equal number of policemen at each place.

So here is the bar.

And what's that bar showing us? That's going to be our whole.

That's 84.

That's the total number of policemen that we have.

Why have we divided it into four sections? Okay, that's because we have four gates.

So we've divided the bar into four equal sections.

Again remember a bar model is only rough.

It doesn't have to be exact.

Because it is that, just a bar model.

The unknown value is how many.

We know there is an equal number of policemen, but we don't know how many policemen were at each gate.

That is our unknown value.

So we can see on our bar model that the relationship between the known and the unknown facts means that we have to divide by sharing.

We need to share out our 84 policemen between the four gates.

So the calculation we would need would be 84 divided by four.

Can you work out what 84 divided by four is? There would be 21 policeman at each gate.

So I've got another example for you.

And this time I have hand drawn a bar model.

Do you want to see it? Okay.

Here is the number story or the word problem.

14 children joined the after-school tag rugby club.

Three times as many children joined the after-school football club.

How many children played football? So we need to work out what the known facts are and the unknown facts.

So the known facts, we have 14 children.

So because I found that out, I put that into a bar.

It's just a small piece.

And then put in 14 underneath it.

Because that block is going to represent those 14 children who joined the after-school tag rugby club.

Then I knew that three times as many children joined the afterschool football club.

So I can take this block that I have now of 14 children.

And because there's three times as many, I'm going to have to multiply that block by three.

So I'm going to need another bar and I'm going to need it longer.

And the label on it is times three.

Because it's 14 multiplied by three.

So the unknown value is how many children played football.

So atop here, I can put my question mark, because this is the bit I don't know.

But already I can see the calculation that I need to work out the answer.

I need to multiply 14 by three.

We can see it here, 14 children, three times as many play football.

So if I calculate 14 multiplied by three, I would have my answer.

I would know how many children played football.

It's time now for your independent task.

These are the steps that you will need to follow, to do your independent task.

Draw your bar model, to represent the known and unknown values in each problem.

Use your bar model to help you choose the correct calculation, to find the unknown and solve the problem.

Remember to write an answer to the question in a sentence.

There's three different problems. I'm going to read them to you.

39 parents came to parents evening to see three teachers.

Each teacher saw exactly the same number of parents.

How many parents did each teacher see? So in your mind, you need to think about what that might look like.

Mr. Slade collected some money from parents for the class trip to London.

He collected four pounds from each of the 27 children in his class.

How much did he collect altogether? Remember all of these are multiplication or division questions.

150 children visited Edinburgh Castle last Sunday.

This was 10 times the size of the group that visited on Monday.

So how many children visited on Monday? Pause the video here whilst you have a go at your task.

And when you're ready, come back to me and I will go through the answers with you.

Well done for completing your independent task.

Okay, let's have a look at the bar models I had drawn.

Let's see how your bar models look similar or different.

So for 39 parents coming to see three teachers.

So I know that the total number of parents coming to see the teachers was 39 and there were three teachers.

They all saw the exactly the same amount.

So my unknown value was the number of teachers.

Sorry the number of parents each teacher saw.

So the calculation is 39 divided by three, which gave me an answer of 13.

The quotient is 13.

So each parent saw 13.

Sorry, each teacher saw 13 parents.

Mr. Slade collected some money from parents for the class trip.

So I know that each child or each parent paid four pounds.

So I made this block here of four pounds.

Then I realised there were 27 children in his class.

So I needed a second bar that showed the whole.

And this was four pounds times 27.

So I multiplied 27 by four and it equaled 108.

So altogether Mr. Slade collected 108 pounds.

150 children visited Edinburgh Castle last Sunday.

So I've drawn a bar here with my 150 children.

This was 10 times the size of the group that visited on Monday.

So I've drawn another bar down here, a much smaller one.

Because I know on Monday it was a much smaller group.

Because on Sunday 10 times as many came.

So I need to now multiply whatever this number is by 10 to get the amount of children who came on Sunday.

So I can reverse this, I can use the inverse.

I can use 150 divided by 10, which will equal 15.

Only 15 children visited on Monday.

If you'd like to, please ask your parents or carer to share your work on Instagram, Facebook, or Twitter, tagging @OakNational, @LauraBehan21, and #LearnwithOak.

Thanks for joining me in this lesson, learning all about bar models.

Now you know that you can tackle any word problems to do with multiplication and division and draw a bar model to help you solve it.

Hope to see you again soon.

Bye bye.