Lesson video

Okay guys, welcome to our next lesson which is using bar models to represent addition and subtraction word problems. So we're going to be using all of our knowledge from the previous lessons to now draw our bar models and get a calculation out of it and actually get answers from them.

Okay, so we're finally on the next, on the final step to work out these answers in addition and subtraction.

So let's start with our lesson agenda.

First we're going to be matching bar models for non-standard contexts so that means its got nothing to do with mass capacity or length.

Okay.

So no units.

We're going to be identifying the correct calculation for a bar model which will then get you guys ready for your independent task and you can come back and check your answers with me.

So you will need a pencil and a ruler to draw your bar models.

A rubber for any mistakes and obviously your exercise book to put your wonderful work in.

So let start.

Matching bar models for non-standard contexts.

So, let's read the question first.

Melvin had a collection of 96 marbles but then Addy gave him some more.

Altogether Melvin had 134 marbles.

How many did Addy give him? Okay so let's ask these questions then.

So what do we know? Well, what's our parts and what's our wholes? Well, altogether Melvin had 134 marbles so therefore our whole is 134.

And we know that one of our parts is 96 marbles.

We know that its, the relationship here is that there is two parts within that same whole.

In that case, our bar model should look like this.

Okay.

Now this is what we were doing last lesson so we should be confident.

The next step now is, is looking at what calculations we get out of them.

These are three possible calculations, okay, that we can answer.

Does this represent 134 take away 96? 134 plus 96? Or 96 take away 134? So, lets see which one it is.

So I know that my part, part whole model is part, part whole.

And in a part, part whole model, I need to add my two parts to get my whole.

Okay.

In this case, I already have my whole.

So I know it's not the addition question.

Okay.

I also know that because 134 is my whole, in order to get another part, I need to do a whole take away a part.

In that case, it's going to be this one right there.

134 take away 96.

Please be careful with 96 take away 134 because subtraction is not commutative, you can't write it either way.

Okay.

Lets move on to the next one.

Melvin had a collection of 96 marbles but then Addy gave him 134 marbles.

How many marbles did they have altogether? Okay so we know our two parts here.

We know 96 marbles and we know 134 marbles.

What we don't know is, is our whole.

So in that case, our bar model should look like this.

So what calculation does that represent? Well as you know, in order to get our part, part whole model, it's part, part, whole.

Now in order to get our whole, we need to add our parts together.

So in that case, it will be 134 plus 96 gives us our whole.

Let's go on to the next one.

Okay.

So, Addy had a collection of 134 marbles but Melvin had 96 marbles.

How many more marbles does Addy have? Okay so, first we need to know what do we know and what we don't know.

So we know that 134 marbles is our whole.

Okay.

And one of our parts is the 96 marbles from Melvin.

Now, what do we not know? Well we don't know one of our parts.

So we know our whole, one of our parts and we're missing another one of our parts.

So therefore our bar model should look like this.

Now the reason why you have two bar models on top of each other is because we are now comparing two values.

It is not two parts within a whole.

Remember that, okay? That can be kind of tricky sometimes.

So, what calculations can we get out of this? So I know in order to get this part right here, a part from my whole.

In that case, it will be 134 take away 96 to get it.

And that is the calculation for this bar model.

Well done guys.

Your turn.

Right.

Here we go.

Excited for this.

This is two parts, okay? So the first part, lets read the question.

So, Pierre scored 22 goals this season.

Great season.

Alexander scored 10 goals.

Not as good.

But I'm sure he created enough assists.

How many more goals did Alexander need to equal Pierre's record? So how many more did he need to get 22 goals? So this is your time now.

You're going to pause the video.

I've just left those questions there for you, to help you.

You're going to pause the video and you're going to choose your option.

Off you go.

Okay.

Back to me.

So, the right answer should've been.

Option number one.

Okay.

So that should be your bar model, that's what it represents.

Because you are comparing two different values.

You know your whole is 22 and you know that one of your parts is 10.

We're trying to find the other part.

Lets go on to the next part.

So thinking about the same bar model, I'd like you to choose the right calculation for it.

So pause the video and then come back when you're finished.

Right, lets find out the right answer.

And the answer is.

Option number two.

Good.

Okay.

Remember our part, part whole model? Part, part, whole.

In order to find out one of the parts, we need to do whole take away a part.

In this case, its 22 take away 10.

Well done guys.

Let's move on to the next part of our lesson.

Identifying the correct calculation for a bar model.

Last term, Melvin's team won 167 more team points than Addy's team.

Melvin's team won 584 team points.

How many did Addy's team win? Now in the examples we're about to do now, I've purposefully put in words that might confuse us.

Lets see if we can identify them as we go along.

So first question, what do we know? Well we know that our whole is 584.

Okay.

Because that's the points from Melvin's team.

We also know that there is 167.

So Melvin's team won 167 more.

Okay.

And what do we not know? Well we don't know Addy's team's value.

That's what we don't know.

Now the tricky word here, that might confuse us, is "more".

Now because the "more" is there, we might decide, okay well, maybe I have to do our 484 plus 167.

But that is not what it's asking us for.

Okay.

Because we know 584 is our whole.

And we know that Addy's team is one of the parts.

We need to find another part.

So we represent it like this, okay.

Therefore, our bar model will look like that.

So watch out for those words.

Okay so now that we have our bar model, lets have a look at the calculations it represents.

584 take away 167.

Well done guys.

Now you guys are going to help me with the next one.

So, watch now for the tricky words.

Melvin completed Level 14 in his game but had 125 points taken away for not finding all the treasure.

Wow okay.

Must've been a tough game.

His final score was 367.

How many would he have scored if he'd found all his treasure? Right, so what do we know? Well we know that one of the parts is 367 because that is the amount of points he was left with.

We also know that he was deducted 125 points.

Okay.

Now what we don't know is actually our whole here.

Because we want to know how much he had to begin with.

Okay so, "would he have" had, that is the key word there.

Now what's a tricky word here.

Well the tricky word here is "taken away".

Okay.

Because when we see that, sometimes we think take away, subtract.

That means that I need to maybe take away 367 take away 125.

So be careful with these words.

They put them in there just to check your understanding.

Okay.

Now you guys won't fall for it, because we're practising them right now.

So, if we know two parts, okay? And we need to figure out a whole.

Then we know that our bar model will look like this.

Two parts make one whole.

Now, what calculation does it look like? Well I know from my part, part whole model, part, part, whole.

In order to get my whole, I need to add my two parts together.

Therefore 367 plus 125 is the calculation we should get from this.

Awesome guys.

Right now its your turn.

So, first we're going to read it.

Buttons scored 536 points by completing Level 15 in his game but he had some points taken away, remember what we found out about "taken away", for not finding all the treasure.

In the end he scored 398.

How many points did he have taken away? I would like you to pause the video and I would like you to answer the question for me now please.

Right.

Lets see how you got on.

The answer was.

Option number 3.

Okay so let's find out how we got to the answer.

So what we know is, when he finished a level, he was given 536 points.

Okay.

So that's we can say that's our whole.

We know that then he was deducted points and he was left with 398 points.

Okay so that's one of our parts.

Now what we don't know is is how much was taken away which is the other part.

Okay.

How much was taken away? Therefore our bar model should look like this.

Now the reason why we don't have two bars is because we're not comparing two different values.

We have got two parts in one whole here.

So therefore our calculation should be 536 take away 398.

Because remember, in order to find out a part, we need to take away a part from the whole.

So, independent task time.

You guy are going to use all your skills that we've learnt to find out the calculations for these four word problems. Remember to follow those steps and pause the video, go to the worksheets and then come back here where I'll be waiting for you to go over the answers.

Good luck.

Right guys.

Right guys, I can't wait to see your answers.

So, we'll read it first.

Buttons and Addy compared how much water they drank in a day.

Addy drank, hold on - reminds me to drink my water.

Addy drank one litre and 750 millilitres.

This was 200 millilitres more than Buttons.

How much water did Buttons drink? Okay.

Right so, we know that Addy drank the most, so then he's going to be our whole.

That's something we know.

We know our whole.

We also know that one of our parts is 200 millilitres.

Okay.

Because that's how much more that was drank.

What we do need to find out, what is not known is how much Buttons drank.

Okay.

So we know that our whole, we know one of the parts, what we don't know is the other part.

Now the tricky word here is "more".

Because when we see "more", we might think "okay we need to add".

So what I'm going to do is I'm going to add my two values together.

Now that is not the case, okay.

We need to draw it like this.

We know that our whole is one litre and 750 millilitres.

We know that one of our parts was 200 millilitres and we're trying to figure out how much Buttons drank.

In order to find out this part, okay, we need to do whole, a whole take away the part that we know.

Which is one litre and 750 millilitres take away 200 millilitres.

We're going to go back to our last lesson when we were adding and taking away with mixed units.

So what do I do first? I collect my like terms. In this case, one litre was by itself, So I collected 750 millilitres take away 200 millilitres which left me 550 millilitres.

Therefore my final answer was one litre and 550 millilitres.

Well done guys.

Lets go on to the next one.

Okay.

Melvin and Buttons volunteered to collect rubbish from the school field and they weighed their bags at the end.

Melvin collected one kilogramme and 200 grammes less rubbish than Buttons.

Melvin's bag weighed one kilogramme and 600 grammes.

How heavy was Button's bag of rubbish? So what do we know? Well we know that Melvin's bag weighed one kilogramme and 600 grammes.

What else do we know? Well we know that Melvin collected one kilogramme and 200 grammes less than Melvin did.

And what we don't know is, is how much Buttons bag of rubbish was? Okay.

So in this case, Melvin's bag of rubbish is our whole.

We know how much Melvin collected and we know that it was one kilogramme and 200 grammes less than what Buttons' bag was.

Now the word you have to look out for is "less" because what we could do is, is we could easily just take away those two known values, and that's not what we're doing here.

Okay.

We know the two parts and in order to find out the whole, we need to draw our bar model like this.

Now what is our calculation going to like? Well in order for us to find the whole, we need to add the two parts together.

So therefore, it should be one kilogramme and 600 grammes plus one kilogramme and 200 grammes.

Now, back to what we knew before in terms of adding and subtracting mixed fractions.

We need to collect our like terms. So that's one kilogramme and one kilogramme and 600 grammes and 200 grammes.

Okay.

We then add them together to then get two kilogrammes and 800 grammes.

And that is our final answer.

If it doesn't look like mine, fix it now guys.

Lets move on to the next one.

Well done.

In April Addy and Melvin collected two kilogrammes and 250 grammes of cans for recycling.

Love the recycling.

I hope we're all recycling at home.

They collected even more cans in May.

Altogether during April and May they collected five kilogrammes and 600 grammes of cans.

What was the mass of the cans they collected in May? First question, what do we know? I'm sure you guys are getting tired of me saying that.

What do we know? But we know that altogether in April and May they collected five kilogrammes and 600 grammes.

That means that's our whole.

And we know that one of our parts is two kilogrammes and 250 grammes because that's how much they collected in April.

Now what we don't know is, is what they collected in May.

So that is our unknown.

Now the word we have to look out for here is "altogether" because as you recall in our previous lessons, whenever we saw "together", we normally add the values together, we normally added whatever we knew.

In this case, that is not it.

Remember, it is important to identify what is the parts and what are the wholes.

Now we know that the whole is five kilogrammes and 600 grammes because that is what they recycled over April and May.

So in that case, our bar model should look like this.

Okay.

Now what's our calculation? As you know, our part, part whole model, part, part, whole.

In order to find out this part, we need to do 500, five kilogrammes sorry and 600 grammes takeaway two kilogrammes and 250 grammes.

So what do we do here? We collect our like terms. That's five kilogrammes take away two kilogrammes and 600 grammes take away 250 grammes.

And then we get our answer, which is three kilogrammes and 350 grammes.

That is a fantastic recycling guys.

Right, if it doesn't look like mine, fix it now please.

Let's go to the next one.

Okay.

Last one, here we go.

Melvin has put too much water in his measuring bucket to be able to measure it accurately.

He pours one litre and 500 millilitres of water out into a measuring jug.

Now there is seven litres and 500 millilitres left in the bucket.

How much water did he have in the bucket to begin with? So, what do we know? You knew it was going to come.

Well we know that there is now seven litres and 500 millilitres, so that's a part.

We also know another part, which is how much he poured out of the bucket, which is one litre and 500 millilitres.

But what we don't know is, is how much he had altogether to begin with.

Okay.

The tricky word here, I think, is "water out".

The fact that somethings going out.

Normally when you take something out, we take away.

Okay.

In this case, that's not what we're doing.

Because we don't know our whole.

And we know in order for us to work out our whole, we need to do part, part makes a whole.

So our bar model should look like this.

In that case, our calculation will be, as you know, to get a whole we need too add together our parts.

So we will be seven litres and 500 millilitres plus one litre and 500 millilitres.

What do we do? Collect like terms. Good.

Now, something's happened here, when we collected our millilitres we had 500 millilitres plus 500 millilitres.

Now we know that to be 1000 millilitres.

But that's also one litre.

Okay.

Now what does that leave us with, that left us with eight litres plus one litre.

And because they're like terms, our final answer can be 9 litres.

Alright.

Really good work today guys.

If it doesn't look like mine, fix it now.

Right guys, I'm really impressed with the work that you've been getting on with.

Remember the steps.

What do we know? What we don't know? And what is the question asking us to do? And watch out for those tricky words that might try make you do the wrong calculation.

Remember its important to identify what is the whole and what are my parts.

Good luck for the rest of the day of learning and I'll hopefully see you guys soon.