Lesson video

Hello there.

My name's Miss Brinkworth.

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

Shall we look at the learning objectives together? So what we're going to be learning right in this lesson is measure.

And what we're doing is measuring and calculating perimeter of rectangles.

We're going to be looking at doing that in centimetres and millimetres.

So let's get started.

The agenda for this lesson is, right, what's perimeter? What are we talking about? We'll clear that up.

We're then going to talk about how we calculate perimeter, how we actually work out what it is.

Then it'll be your independent task.

This gives you a chance to apply what you've learned during this lesson.

And then the quiz at the end just gives you a chance to see how many of those you can get right.

All about perimeters today.

So you will need a pencil and a ruler and some paper.

Please make sure you get all of that now.

If you can't find a ruler because you're at home, please don't worry too much.

The lesson should be absolutely fine without it.

So pause the video and get your equipment.

Okay, well done.

Let's get started then.

So we've got a warm up here, and this is just about getting your head back into measure again and getting you to think about centimetres and millimetres.

What are we talking about when we're measuring? So here's some lines.

Look at the lines on the ruler.

Can you estimate the length of each line? So have a go at applying it to that ruler on the screen.

This is because you'll all be looking at screens of a different size.

It'd be very hard to put your own ruler against against the screen.

So just using the ruler on the screen there, estimate the size of those lines, and estimate means have a really, really good guess.

So pause the video, take as long as you need.

Okay, well done everybody.

Now as these are estimates, yours will not be identical to mine because we're guessing.

We're having a good guess by looking at those lines.

As long as you're somewhere near what I've said, as long as you're not miles away, much bigger number or a much smaller number, then you've done a really, really good job.

So here's the estimations I came up with, and like I said, as long as you're near them, that's absolutely fine.

It's a really good idea just to remind ourselves what we're talking about.

So when we measure, we are measuring small distances today.

So we're talking about centimetres and millimetres.

That's what we use to measure those small lines.

There are 10 millimetres in every centimetre.

If we were talking about a bigger, if we were maybe measuring the room, we might talk about metres.

We won't be talking about metres today cause we'll only be measuring those small lines today as we measure perimeter.

Okay, so what is perimeter? How do we calculate it? And what are these shapes called? So how would you calculate the perimeter of these shapes? What are these shapes called? Now, hopefully you can see that all these shapes have got four sides.

That means that they're all quadrilaterals.

They've got something else in common as well.

They are all rectangles.

Now that might seem a little bit confusing, because you're going to say, "Hang on a minute, Miss Brinkworth.

"That orange one there is definitely a square." Now, squares are rectangles.

The way of thinking about them is being in the same family.

You could think of the rectangle as their surname.

Rectangles means that they all have four sides and they all have four right angles.

So any shape with four sides and four right angles is a rectangle.

There are different types of rectangles.

They differ within that family, just like you might be different from your brothers and sisters, but they're all rectangles.

So what are we talking about when we talk about perimeter then? So today's lesson is to measure the perimeter of rectangles.

So what actually is the perimeter? Well, the perimeter is the distance around the edge of the rectangle.

So it is the distance around all four sides.

It's known as the boundary and it is the perimeter.

And when it comes to rectangles and perimeters, there's a really clear, simple way of measuring the perimeter.

So here's a square.

So let's start with this square, which we've just said is a type of rectangle because it's got four sides and four right angles.

What else do you know about a square then? What makes a square different to other rectangles? Hopefully you can see that what makes it a square is that it's got four sides which are all the same length.

All sides are equal.

Now, this makes measuring the perimeter really easy because if we know the measurement of one side, because they are all equal, we will know the measurement of all the sides.

So if we're told that one side is six centimetres, then we know that side is six, and the other side, and the other side and the other side.

All squares have four sides.

So if we're told the measurement of one, all we have to do is take that measurement four times.

Six, add six, add six, add six.

Hopefully you can see that that's 24, but hopefully as well, you can see that we know a much quicker way of working that out.

We don't need to do repeated addition.

We don't need to do six, add six, add six, add six.

That takes a long time.

It takes a long time to write out, and when something takes a long time to write out, there's a lot of error there; a lot of room for error, sorry.

We could add it up slightly differently, or we could miss one out or add one too many.

So we know there's a simpler way.

And this is where our fantastic times tables come in handy.

So hopefully you also can see that six times four is 24.

It's six times four because each side measures six and we've got four of them.

Six times four is 24.

So when we are working out the perimeter of a square, where all the sides of the same, we take the measurement of one side and times it by four.

That way we'll have got the measurement all the way around the outside of the square.

Will you have a go on your own? It says here that this side measures four centimetres.

One side is four centimetres.

Pause the video here and work out the perimeter of the whole square.

How did you get on? Hopefully, you can see that this is a nice, simple strategy, a nice, simple success criteria for working out the perimeter of a square.

What do we need to do with that information we've got of one side measuring four centimetres? Well, we just need to times it by four.

So we could do repeated addition if you wanted, and there you can see that we've got our four sides: One, two, three, four fours.

Four fours is 16 because four times four is 16.

And another way of writing that is four squared.

So that little two that we've put above the four there is four squared.

That means that we timesed four by four to give us 16.

Okay, now this shape is slightly different, this purple shape.

Can you see what's different between the purple shape and the orange shape? It's an oblong, the purple shape, and that's because it doesn't have four sides which are equal.

But, it does have pairs of equal sides.

So in this oblong, you can see that the top and the bottom are longer, but they're equal to each other, and then the two sides are shorter, and again, they're equal to each other.

So how do you think we work out the perimeter of this shape? We can see that a square has got equal sides and oblong's got two pairs of equal sides.

So, normally when we're given a rectangle, we'll probably be given the measurement of both sides, of two sides.

This is because we can use that to work out the opposite one.

So we only need to be given the measurement of two sides, and that's because the other two are equal to them.

Let me show you what I mean.

So for this one, if we know that the top is eight, then the bottom is also eight, and if we know the side is four, then the other side is also four.

So we need to add together all of the sides, and we know that it's eight and eight and four and four.

So two lots of eight, two lots of four.

And then we'll have the whole of the rectangle.

We'll have taken in the measurement all around the outside.

So to work out with you, eight add eight, add four, add four, which gives us 24.

We can do that as a multiplication.

Eight times two, add four times two.

So we can just use our two times table.

We can do four times two, eight times two, add them together.

We've got the whole rectangle.

Okay.

Your turn.

One side is 11.

One side is three.

What is the perimeter of this rectangle? How did you get on? Well hopefully, you did 11 add 11, or 11 times two, and three add three, or three times two.

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

If you want to do the three times three first or the 11 times 11 first.

Sorry, 11 times two, three times two.

That's absolutely fine.

It doesn't matter which order you do them in.

It doesn't matter if you add the top and bottom first or the sides first.

You are still taking in the whole rectangle.

So you could also do three times two, 11 times two.

That's the quicker way.

But if you would prefer to do the repeated addition, that's also fine.

Okay, independent task now.

So go away and have a go at the worksheet on your own.

Take as long as you need and then unpause the video and we'll go through the answers together.

How did you get on? So here's the answers.

I'm not going to go through them in too much detail, just because it's a bit boring, but I will put them up there for you to have a look and see how you got on.

If you made any mistakes, have a look at where that mistake crept in.

Maybe you didn't multiply each side by two, or as four, as you should have done, but have a think about where you made mistakes.

Cause that's where the real learning happens.

Okay, and I hope you got into the challenges.

All right, should we have a look at that together? Now, that shape to me looks like a square, that orange one, the first one, and squares are great because they've all got sides, which are the same.

So there's only one answer that we can have for that orange square.

And to get that answer, we need to take the whole perimeter.

We've been given the perimeter, and now we need to work out the sides.

So it's sort of working backwards to what we did in the bulk of the lesson.

So instead of timesing, we're dividing.

We've got the perimeter and we need to work out the length of one side.

So 48 divided by, well, what are we going to divide it by? We're going to divide it by the number of sides that that square has.

So 48 divided by four.

Hopefully, you know your four times table quite well.

48 divided by four is 12.

Really well done if you go that one right.

The other question is slightly harder, just because there's a few right answers.

So we've got a rectangle and the perimeter is 26.

So we need to split that 26 up, don't we? To find two longer ones and two shorter ones.

Now there's lots of different combinations you could have.

As long as you've got two numbers which when doubled add together to make 26, you're doing absolutely fine.

Here are some.

You might have 10 add 10 is 20 and then three add three is six, or you might have eight add eight is 16 and then five add five is 10.

I cause I should've written that in for the answers.

Really, really well done for having a go at those.

If you got different answers, please share them with us.

We'd love to see your work, even if you got exactly the same answers.

Any of your working out, we'd really love to see.

So if you'd like to, please ask a parents or carer to share your work on Instagram, Facebook, or Twitter and tag @OakNational #LearnwithOak.

But please, before you go, do have a go to that final knowledge quiz and see how well you got on with today's learning.

Really well done, everybody.

Please enjoy the rest of your day.

Bye-bye.