# Lesson video

In progress...

Hello welcome to our next lesson using bar models for addition and subtraction word problems. Okay so let's start with our lesson agenda.

First we will be reviewing bar modelling okay? Just see what we can remember making sure we understand what their purpose are for.

Then we're going to be matching bar models to the problems which will get you ready for your independent task and then we can go through the answers.

Now you will need a pencil a rubber and an exercise book to complete the task given to you today.

So let's start with reviewing bar modelling okay? What do we know about bar modelling? What is it used for? Why? How do we use it? Have a look at these examples down there and take a minute to just reflect what is each one showing? What operations are we doing? Are we doing addition, subtraction, takeaway or division? Okay so let's have a look at them each.

Okay so let's have a look at them each.

So we have this one right here.

And as you can see you can see one whole and it's got how many parts? One, two, three, four, four parts.

Now this is the really important thing the first thing I look at when I think about bar modelling is parts and wholes okay? Now the whole is unknown and the one part is known as 12.

This bar model over here.

Well this is one whole okay? But it's split into two parts.

Now in this case the whole is known as 134 and one part is known as 96.

And the unknown is the smaller bar right here let's move on to this one.

We have one whole okay? Which is all split into how many parts? Two parts, we know the two parts but we don't know the whole okay? And I'm really just being specific with the language I'm using today.

Over here we have a bar model with two separate bars okay? These have all been a one bar one single lines has been two.

That means that we don't know the whole here, but we know the value of one of the parts.

Now what this line tells us, it has been divided by three.

So this whole is divided into three to get these parts here.

Why do we use bar modelling? Well, it helps us to show the relationship between the known and the unknown values in a problem, which is why I kept saying I know and I do not know.

it can be a representation of a word problem that helps to identify the calculation needed to solve it.

So sometimes when we get word problems which is really difficult to decipher it.

And I find it best to actually draw out the bar model so I can see it, it's right in front of me and it is a visual representation of what the word problem looks like.

And that makes it easy for me to process and to understand.

And finally, it helps to identify there is a comparison between two or more values or if there are part-whole relationships or scaling relations between values.

Now all of this words might be new to you but we're going to learn about them today.

So let's get started matching.

Matching bar models to the problems. So in this part, we're going to be given a word problem, and then the choice of bar models, that one of them represents that word problem when we have to decide.

But there's question is that we have to ask ourselves before we do that, what are the known values? What are the unknown values? Are the values part of a whole? Is there a difference between two values? And are we making a comparison? Okay so, so let's start with this one.

Buttons had a bag of raisins that weighed 57 grammes Melvin had a bag of raisins that weighed 40 grammes.

How much heavier was Button's bag compared to Melvin's? So we need to ask ourselves, what is it that we know? So here we go it says the known values are 57 grammes and 40 grammes and the problem is making a comparison between the two values.

So we've identified what we know, what we don't know and what the problem is asking us to do which in this case is a comparison.

Now the values are not parts of a whole, so the unknown is the difference okay? So, because it's not part of one whole, we know that it is going to be the difference so that means we're going to need two bars okay? So now I've just highlighted on a word problem much heavier because that's where we're thinking about comparison and the difference okay? So the difference between the two values so this is the correct bar model.

So if we're looking at that one then it must represent this bar model here because the values are not parts of a whole, and these two are parts of a whole okay? And in this case, we are comparing the difference between two values 57 and 40.

So we need to work out the difference between 57 and 40, which is 17 so Button's bag is 17 grammes heavier than Melvin.

Addy and Melvin measured the height of their sunflowers.

Addy's plants measured 153 centimetres Melvin's plants was 203 centimetres how much taller was Melvin's plant? So what do we know? We know that Addy's plants was 153 centimetres we know that Melvin's plant is 203 centimetre So that's what we know, what, what do we not know? What is unknown? How much taller was Melvin's plant.

So what we need to, what we don't know is the difference between their height.

So again, we are comparing heights of a plant.

So in that case, the answer should be this one right here okay? Because we have 203 as our whole and we know one of the parts which is 153, and we're trying to work out this unknown right there.

Let's move into the next one and see we get up.

Read it first okay? Button's weighed his chocolate buttons okay in March they weigh 203 grammes, so that's something we know.

At Easter he was given another 153 grammes of chocolate buttons wow! to be brushing his teeth he's going to get rotten teeth if not.

what was the total weight of Buttons chocolate button collection? A lot of buttons in there, honestly right, so what do we know? We know that the original bag weighed 203 grammes, We know that and then he was given another bag of 153 grammes so this is what we know and what we don't know, what we're trynna find out is the total weight of the chocolate Button's and collection okay? So in this case, we have got two parts and we don't know the whole okay? So if we look at our bar models, where do we have two parts and with an unknown whole? And it would be two parts and we don't know the whole so in that case, it is this one right there okay? And can you see, we identify what we know, what we don't know and then we see whether it is part of two parts of a whole, or if you're comparing differences, well done guys let's move on to the next one.

Okay, your turn let's read it first, Mr Slade kept a record of the amount of water drunk by the class gerbil.

At the start of the day there was 203 millilitres in its bottle.

By the end of the day there was 153 millilitres left.

That's really good from the gerbil drinking water is important guys.

How much water had the gerbil drunk? Okay remember what you do first what do you know, what do you not know, what is the question asking you to do and then have a look at the bar models to see which one it matches to.

Pause the video now, and then come back for the answer.

Okay you're back to me are you ready to reveal the answer? The answer is boom option number one, okay let's find out why.

So we know at the start of the day, if he had 203 millilitres of in a bottle and by the end he had 153 millilitres in a bottle so, this means that our 203 millilitres is our whole.

So in these bar models which one, where does it represent as a whole? This one it doesn't because it says that the whole unknown in option two it does and so does option one, okay, so we're left with option one and two here.

By the end of the day, there was 153 millilitres left that means that's one of our parts and it's similar here.

How much water I had the gerbil or drunk? Now, the reason why it's this one and not this one is because we are talking about two parts within a whole, okay we know that this 203 millilitre is the bottle okay? So we're talking about two parts within that whole and that's why option one is the answer.

Because this is how much is left, this is how much he drunk within the bottle of water.

In this case, you're comparing two different things, if it had been the gerbil or drunk 203 millilitres in the day, and the pet rabbits had drunk 153 millilitres in a day, then you are comparing two different values here, which is why this is the right answer.

Right so it's time for the independent task.

What I'd like you to do now is, is you're going to go to the worksheet and read through the word problems and you're going to ask yourself those questions.

What do you know? what do you not know? What is the question asking me to do? I'm I comparing differences? Is it adding to make a whole, two parts to make a whole? Okay, and you know or is it that you know a whole and you know a part but you need to find out another part with okay? So pause the video now good luck with the independent task and then come back to me for the answer when you're finished.

Okay back to the answers guys as always we start by reading up what problems so Ant and Dec weighed the mass of their parcels.

Ant's parcel weighed 450 grammes, Dec's parcel weighed 870 grammes.

How much heavier was next parcel? So what do we know? Well, do we know our whole? Yes, in this case, our whole is 870 grammes.

Do we know any of the parts? Yes, we know one part is 450 grammes.

So by knowing the whole is 870 that means that it's definitely not going to be this one.

Okay so it's either this one or this one okay? Now how do I distinguish which one of the two is, well, this one is comparing two different values and this one right here is the whole, the same whole divided into two parts.

Now what are we doing? Are we comparing two values or is that the same whole into two parts? You're right it is in fact, this one right there okay? We are comparing the difference of two different values.

So we have 870 grand as our whole and we have 450 grammes as our parts.

So this is the bar model that represents well done guys, let's go to the next one.

So Pierre took an enormous chocolate bar with a length of 106 centimetres to Alexander's house and accidentally left it there.

When he returned to get it, he noticed the length of the chocolate bar was 67 centimetres.

How much chocolate was eaten? And who ate it? Well, I reckon that was Alex, but let's find out that's not what we're here to do, although I'm quite annoyed I'd be quite annoyed about that to be honest.

So what do we know? Do we know our whole? Do we know that our whole? Yep, we know our whole is 106 centimetres.

Do we know any of the parts? Yep, we know that one of the parts is 67 centimetres, that means that we are looking for the other parts.

So if we know the whole is 106 centimetres, then that means that it's either going to be this one or it's going to be this one okay? That rules, this one out in the middle.

Now, they both show that the parts are 67 centimetres but why? But which one is it? Well, we know that the chocolate is the whole okay? And parts of that whole has been taken, we are not comparing the difference of two different values here.

So therefore it is going to be this one.

So the whole chocolate, which is the whole bar here is 106 centimetres.

And this part here was eaten probably by Alex, and this is what was left and that's how we find this out.

Well then guys, kind of makes me want to eat chocolate now, but definitely not going to be eating it around Alex.

Right onto the next one here we go, Jack and Jill went up the hill to collect some water.

Jack collected for.

Oh, it doesn't rhyme does it? Jack collected 490 millilitres of water and Jill collected 835 minutes of water.

How much water did they have all together when they went tumbling down the hill? Now that all together is really important okay? Because in this case, it means that we are adding the two values together.

What do we know? We know that one of the parts is 490 millilitres and we know that one of the parts 835 millilitres and we need to find out the whole.

That is what we don't know, we don't know the whole, so let's have a look well, this is the only one where we don't know the whole okay, this is where we have the two parts unknown And we don't know the whole in that case, that is a bar model.

Really good word today guys, we're just starting off to understand how we represent them.

And I really hope that if it's nothing you don't understand you can go back into the lesson and just go over those steps.

Whenever you see a word problem, what do we know? What do we not know? What is it asking us to do? Okay, and then we can represent it in these bar models.

I hope you feel less confident with using bar models now, thank you so much and good luck with the rest of your learning today.