Lesson video

Right, welcome to our next lesson where we are actually going to be drawing the bar models to represent the word problems, similar to our previous lesson.

Let's get started.

Okay, our lesson agenda.

So, we're going to start by adding and subtracting in mixed units.

Then, we're going to be drawing our bar models to represent word problems. So, then it prepares us for independent task and then you can get on with your answers.

All right, awesome, let's move on.

So, you will need today a pencil and a ruler, okay? Because you're going to be drawing your bar models.

A rubber and an exercise book.

So, adding and subtracting in mixed units.

So, I have a question, okay? If I had one, two, three apples, okay? And I had one, two oranges, okay? How would you describe them, okay? If I had these fruits here, would you say, oh, can you please pass me the five orange apples please? Or can you please pass me the five apple oranges? You wouldn't add them together, would you? You can't add apples with oranges and you can't add pears with oranges.

You'd have to say there are three apples and two oranges, okay? And I just want you to remember that when we are adding in mixed units, because you can never, ever add units that are different.

So, we have 2kg and 400g, plus 1kg and 370 g.

Now, this is what I don't want to see, okay? 2kg and 400g plus 1kg and 370g.

Okay, so that's two, plus 400, plus one, plus 370, equals 773 kg g.

That is incorrect guys.

We never do that, you can never add numbers if its mixed units, remember that, okay? Remember, apples, don't add apples with oranges.

So, in that case, I'm going to show you how we do it today.

We're going to follow some steps, okay? So, we have the same questions as before, and the first thing we do is that we're going to group the like terms. So, we're going to group our kilogramme, and we're going to group our grammes together.

So, therefore we have 2kg and 1kg and we have 400g and 370g.

Second step, we're going to add the like terms together, okay? So, we have 2kg plus 1kg, which we can add because they have the same units, which is 3kg, and 400g plus 470g is equal to 870g because they have the same units.

Finally, our answer is you bring them together and it's 3kg and 870g.

Please don't, after all that work, go three plus 870 equals 873 kg g.

We cannot add numbers with different units.

Okay, moving to the next one.

Right, so, 3L and 550ml, takeaway 2L and 220ml.

First step, we group our like terms, okay? And that's 3L and the 2L and the 550ml and the 220ml.

Then, because we're subtracting here, we're going to subtract.

Then, because we're subtracting here, we're going to subtract the like terms together.

So, 3L take away 2L is equal to 1L, and 500ml take away 220ml is equal to 330ml.

Therefore, the answer is 1L and 330ml.

Right, I think you guys are ready to try this by yourself.

So, are we ready? Here we go.

3kg and 350 g plus 4kg and 515 g.

I'd like you to pause the video and I'd like you to answer this question.

Don't forget our steps, first step group like terms, second step, add or subtract your like terms, and finally, answer.

Off you go.

Right, back to me.

So, the answer should have been 7kg and 865g Let's figure out how we got there.

So, first step, group like terms, 3kg and 4kg, and 350g and 550g, then add like terms together.

3kg plus 4kg equals 7kg, and 350g plus 515g is equal to 865g.

Ooh, a lot of numbers.

And therefore, the answer is 7kg and 865g.

Well done, guys, we're going to remember this and we're going to use this later on today in our task.

So, let's get started, with drawing bar models to represent word problems. Okay, so let's start by reading a word problem.

"Mr Slade and Melvin we're collecting shells "and weighed the collection each day.

"On Monday, they collected 3 kg and 150 g "and on Tuesday, they collected another 1 kg and 450 g.

"What was the weight "of the shells they collected all together?" So, what do we know? I know that my two parts in this case, is 3 kg and 150 g and my other part is 1 kg on 450 g, okay? What do I not know? Well, I'm looking for the whole, cause I want to know what the weight is altogether, okay? So, I've drawn my two bar models, I'm showing you how to represent them.

And in order to make it look like a bar model, it looks like this, okay? So, my two parts together to make this whole, and that's what we're trying to find out there.

All right, let's move on to the next one.

So, "Melvin and Button's both had a fish tank each.

"Melvin's fish tank holds 3 litres and 250 litres "but Buttons tank holds 700 litres and 500 ml.

"How much more water does Button's tank hold than Melvin's?" So, what do we know? Well, we know that Melvin has 7 litres and 500 ml and we know that Button's is 3 litres and 250 ml.

So, we know that our whole is Melvin, okay? Will be represented by Melvin, and one of our parts is Buttons.

And we need to, what we don't know is that we need to find out what the difference is.

How much more does Melvin have to Buttons? And that's where it is.

Now, we are comparing the differences of two different values here.

And that's why we have two bars, okay? Therefore, our bar model will look like this.

I'm adding all of it together.

So again, our whole, our part, and our parts, okay? We know one of our parts, we know our whole part, but this is the part that we do not know, cause we are comparing two different values.

Let's go into the next one.

So, "Addy had a sunflower that was 265 cm tall.

"Overnight the strong wind snapped the sunflower "and broke off 133 cm." That's really sad.

"How tall is Addy's sunflower now?" Okay, so what do we know? Always the first question.

I know that my whole is 265 cm cause that's how much it was originally, okay? I know that within that same whole, I'm going to be looking for two parts, and one of the parts I know, and that is 133 centimetres, which is why I've drawn it within that same bar, okay? What do I not know? Well, I don't know how much broke off, which is going to be that little space there.

Therefore, my bar model is going to look like this, okay? Remember, that the reason why it is within the same bar is because we're talking about the same sunflower, okay? We're not comparing two different sunflowers, it is the same one, where a part broke off of it.

So, it is two parts within that same one whole.

Okay, so, that means that we are ready for in the pen print task.

You're going to follow all those steps, asking you, you're going to ask yourself all those questions and draw them out in your book.

Now, make sure you're using a ruler when you're drawing, because mathematicians, we use rulers.

We don't draw freehand, and we also use a pencil to draw.

Now, it might mean that you might try some and it doesn't work, it might take a bit of trial and error, but be patient, you can go back into video and have a look if you need anything from me.

But when you're finished with your worksheets, come back to the slides, and we'll go through them together.

I'm sure you guys are going to be great.

Well done.

Okay, welcome back.

So, here we go, answers.

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

"Addy drank 1 litre and 500 ml.

"Buttons drank 250 ml less.

"How much water did Buttons drink?" So, in this case, we have got two values that we are comparing.

That means we're going to have two bars.

That's straight the way I'm thinking about that, okay? So, what do we know? What do we know? I know that my whole is 1 litre and 500 ml from Addy, okay? Because we're comparing with Addy and we know one of our parts is 250 ml less.

Now, what we don't know is Buttons value, Buttons part, right? So, this is how I've separated it.

So, I know my whole 1 litre and 500 ml.

I also know how much less was drank by Buttons, which is why I've got the little curvy bit with 250 ml.

And what we don't know is Buttons.

So, your bar model should look like this, okay? If it doesn't look like mine, fix it now, please.

Remember, we are comparing two values that's why we have two bar models.

Okay, let's move on to the next one.

"Addy and Melvin collected cans for recycling." That's really good that we're recycling, saving the planet, well done.

"Weighing them each month.

"In April, they collected 2 kg and 250 g "and in May they collected another 1 kg and 400 g.

"What was the weight of the cans they collected altogether?" Remember them saying altogether that way, because in this case altogether normally means that we're going to add them together.

In that case, we know that one of our parts is going to be 2 kg and 250 g, and another part is going to be 1 kilogramme and 400 g.

That means that what we're trying to find our unknown value is a whole, okay? So, your bar model should look like this cause we're adding them together, okay? Altogether in this case means that add both our parts to make a whole, so, part, part whole, right? If it doesn't look like mine, fix it now, guys.

Let's move on to the next one.

"Melvin and Buttons, volunteered "to collect rubbish from the school field "and they weighed their bags at the end." These are some great students, I really, really like how much they care for the environment.

It's really good guys.

"Melvin collected 1 kg and 600 g "but Buttons collected 2 kg and 900 g.

"How much lighter was Melvin's bag of rubbish." Okay, so, let's have a look.

We know that our whole, okay? Is 2 kg and 900 g.

We know one of our parts, okay? Which is Buttons, 1 kg and 600 g.

And what we don't know is the other part, which is the difference between Melvin and Buttons rubbish, okay? So, this is what it looks like.

And because we are comparing two values, we have two bars, okay? Two different values, therefore, our bar model should look like this.

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

Let's go into the next one.

Okay guys, let's read this one.

So, "Melvin was given white chocolate "and milk chocolate eggs for Easter." I'm sure he was after all the amazing recycling that he's been doing.

"In total, his eggs weighed 1 kg and 850 g.

"If his white chocolate eggs weighed 675 g, "how much did his milk chocolate eggs weigh," right? So, it seems that we're not comparing two different things here, okay? So, that means, I know I'm going to have one bar model because we're talking about just the chocolate eggs.

So, what do we know? What do we know first? We know that the whole is 1 kg and 850 g, okay? We also know that one of the parts within that whole, okay? The white chocolate, weighs 675 g.

What do we not know? We don't know the value of the milk.

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

Now, remember the reason why it's just a one bar and we don't have to here is because we're talking about the same things.

The same whole is the two parts within the same whole, remember that.

Two parts within the same whole, which is our chocolate eggs.

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

Now, this has been great work guys.

I don't know about you, but I'm really enjoying working with our bar models.

I know that it's, it makes it so much easier for me to understand what problems, when I'm able to draw them out.

Now, I'm hoping that over time, you'll be able to do this in your head and you can almost imagine the bar models when you see these questions, but let me reassure you the mathematicians and all your math teachers will still use this today just to help them understand more difficult questions, okay? Well done for your work today, have great learning for rest of the day.