# Lesson video

In progress...

Hi there everybody My name is Miss Brinkworth.

I'm going to go through this math lesson with you today.

Let's look at our learning objective.

We're going to be comparing and calculating the area of rectangles using square metres.

So hopefully we've been pulling on a lot of the knowledge that you already know in terms of what area is and how we calculate it.

And we'll be applying that to a new unit measurement, which is metres squared.

So let's have a look at our lesson agenda.

So what we're going to be doing is talking about how we calculate area.

Then we're going to look as well about how we find missing lengths.

So we will be working backwards.

It'll be a calculation where we've been given the area and we need to take from that what the missing length might be.

They'll then be time for you to have your chance at an independent task to work through some of these calculations independently.

And then at the end, there'll be a quiz as well.

A few questions for you to work out how well today's learning has gone on.

So let's get started.

All you're going to need is a pencil paper and a ruler if you can find one.

Please don't worry too much if you cannot find a ruler.

It's absolutely fine But pause the video here and make sure that you've got the equipment you need.

Wonderful.

Let's get started.

So as a little bit of a warm-up, I'd like you to have a think about how many different shapes you can make with an area of six units.

So units are just these little squares that we're using.

You can think of them as centimetres squared or metres squared.

And what I'd like you to do is just move those squares around, draw them out on your paper, and think about all the different combinations of shape you can come up with that have got an area of six.

Pause the video.

Maybe just give yourself two minutes and see how many you can find.

Well done, for having to go that warm-up, everybody.

So you're basically doing an investigation here.

How many different ways can we create a shape with an area of six units? Here are some that I came up with.

Yours might be different, or you might have some that are the same as mine.

They might be in a different orientation, they might be on their side or upside down, but there are so many different ways that you can move around six different units.

So hopefully this has shown you that shapes with the same area can look very different.

So let's move on to what we're going to be doing today.

So we're going to be calculating the area of rectangles.

Can you remember what formula we need to calculate the area of rectangles? Well, what we do is we times together, we multiply, the length and the width.

So for this rectangle, we'd be talking about 3 times 21, or if you'd prefer, 21 times 3.

We know it doesn't matter which order we do those multiplications in.

So the area of this rectangle, the surface, the space that it takes up, is at 63 metres squared.

I know that I need to put metres squared because that's what the sides were measured in.

They were measured in metres.

So when I change that to a 2D measurement of area, I put metres squared.

How to work out 3 times 21? That's up to you Whether you want to do repeated addition, whether you went to partition 20 and one and multiply the tens and the ones separately, or if you want to do a bit of short multiplication.

Any of them are fine, as long as you get the right answer, 63.

Okay.

So our formula for today that we are looking at is area is length times width when we're looking at rectangles.

Pause the video here and have a go at multiplying the length and the width to find the area of these rectangles.

All of the units are going to be metres squared because all of the lengths of the sides you've been given there are metres.

So pause the video, and take as long as you need to work those out.

Really well done.

Hopefully you're feeling quite confident now in how to work out the area of rectangles.

So let's have a look at that green one.

We have got 6 times 8.

So 6 times 8 is 48.

If you'd prefer, you can think of that as 8 times 6.

Doesn't matter which order you do those in.

How do you remember 8 times 6? Do you think about it in your eights or your sixes first? Do you use a fact that you're really confident with, like 6 times 6, and change it from there? or even 10 times 6 and take 12 away? Whichever way you think about getting the answer for 6 times 8, well done if you've got 48 for that one.

And remember that it's metres squared.

For the grey one, we're talking about 7 times 2.

No, sorry It's 7 times 4.

The reason I said 7 times 2 is 'cause that's where my brain always goes when I see 7 times 4.

I do 7 times 2 is 14, and I double it for 28.

And again, it doesn't matter which order you do that multiplication in.

You're going to get the answer 28 metres squared.

Now, that light blue shape, why have we only been given one measurement, only one side measurement? Well, it's because it's a square, isn't it? And what do we know about squares? We know that all the sides of squares measure the same amount.

So if one of them is seven, they must all be seven.

So to work out the area of that one, we need to do 7 times by 7.

7 times by 7 is 49.

It's good to have those facts, the square number facts, so a number of times by itself, quite confidently 'cause you can move around from those.

So 7 times by 7 is 49.

If you looked at that question and you thought, "I can't do it.

They've only given me one side measurement." Next time you come across a question you think you can't do, just go back to it and think systematically.

They will have given you all the information you need.

So you think to yourself, "Why would they only have given me one side? How could I possibly work it out with just one side measurement?" And then hopefully you'll think about it being a square, and you'll have another go at getting that answered.

The last one, then, that dark blue rectangle, 5 times 6 is 30.

So well done if you've got all of those right and got metres squared for all of them.

It is important to write down the unit and get that correct.

That's because that's the really accurate correct answer to the question.

6 metres times by 5 metres gives us 30 metres squared when we're working out area.

And it shows that you really understand that area is a measurement of 2D space.

Okay.

Remember, you can do that in any order.

So this time we need to sort of work backwards.

We've been given the whole.

The area is the whole, and we've got that in this question.

We need to work out one of the parts.

How do we make that whole? So actually, instead of this being a multiplication question, as we've been looking at, it's now a division question.

Division questions start with the whole and work back to find the parts, but thankfully, we can still use our multiplication to help us.

So what's happened to three if I've ended up with 24? Well, 24 divided by 3 is 8.

3 times by 8 is 24.

So that's our missing side there.

And the correct units when we're finding a missing side is just metres for today, not metres squared, because we are finding a side which is a length and a distance from one point to another.

So instead of squared, it's just metres.

So have a go here at finding the missing side.

Remember that what you need to do is a division question today.

So take the area divided by the side you have, and you'll find your missing side.

Well done, everybody.

Let's see how you got on.

24 divided by 6.

How many sixes are there in 24? What do I need to times 6 by to get to 24? Well, hopefully you know your six times tables quite well, and you know that 24 divided by 6 is 4.

6 times by 4 is 24.

So you're missing side for that green rectangle is four.

To check it, you could always go back to your multiplication question and check that 6 times 4 gives you 24, that length times width gives you your area.

What about the grey one, then? Well, 42 divided by 7.

How many sevens are there in 42? Well, I know that 7 sevens are 49, so it's one less than that.

So it's six.

You're missing side for the grey rectangle is six metres.

And for the blue one there, 18 divided by 3.

How many threes are there in 18? And the answer is six.

So well done if you've got that one right.

Okay.

So for the first part, you need to work out the area.

So for that, it's multiplication questions.

For the second part, you're going to be finding the missing side, and for those, it's those division questions.

So pause the video, take as long as you need, and come back for the answers when you're ready.

Well done at having a go at the independent task, everybody.

I wonder if it was the multiplication or the division that you found easiest.

Really, you should become as confident with both as each other because you're always using your multiplication knowledge.

Whether it's multiplying or dividing, it's the relationship between the same numbers.

But let's go through them and see how well you got on.

So for that orange rectangle there, we can see we've got 6 times 9.

Six lots of nine.

What are six nines? Well done if you knew that that was 54.

Moving on, we've got 8 times 7.

I remember 8 times 7 as five, six, seven, eight.

56 is 7 times 8 and 8 times 7, so that's how I remember that fat.

Five, six, seven, eight.

For that light green rectangle there, we've got 13 times 11.

I wonder how you worked that one out.

Well, I know 12 times 11, and I just need to add another 11 onto it.

The turquoise one there, you've got 16 times 10.

So I'd probably think about this as 16 made 10 times bigger, move 16 two decimal places, sorry, one decimal place since we're timesing by 10.

So 16 becomes 160.

Well done if you've got that right.

So how many threes are there in 36.

There are 12 threes in 36.

What about the next one, then, where we have to do to 1,200 divided by 40? Well, I don't know my 40 times tables, but I do know my four times tables.

And I can see that relationship between 12 and four.

So 12 divided by 4 would be 3, so 1,200 divided by 40 is 30.

Really, really well done if you saw that.

For 54 divided by 7, it's, sorry, 54 divided by 9 is 6.

And for your last question there, you can utilise that fact I was talking about earlier with the purple rectangle.

Five, six, seven, eight.

Where here, you've got your five, six, you got 5,600, and you're dividing it by 70.