Lesson video

Hello, mathematicians.

My name is Miss Brinkworth.

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

So if you look at our learning objective, what we're going to be learning to do is calculate the perimeter of rectangles in both centimetres and metres.

So we're going to be looking in detail about what we mean by perimeter and we're going to be looking really closely at that relationship between centimetres and metres.

Hopefully by the end of the lesson, you'll feel really confident converting between one and the other.

So, let's look at our lesson agenda.

So we're going to look at partitioning to calculate the perimeter.

So partitioning metres and centimetres.

We are going to then have a good look at how we convert between metres and centimetres.

You'll have an independent task where you'll have an opportunity to calculate some perimeter independently.

And then it will be the quiz at the end to see how well today's learning has gone in.

So let's get started.

All you're going to need is a pen or pencil, some paper, and a ruler would be quite useful, but we know if you're at home, you might not have one, so please don't worry too much about a ruler.

Just make sure you have got a pen and pencil, that's absolutely crucial.

So pause the video here and get what you need, please.

Okay, welcome back.

Thank you for getting your equipment.

Okay, let's start a warmup then.

So here are some shapes and you're being asked to work out what the length of one side is.

So they've all got equal sides, so you just need to work out the length of one side and you've been given the perimeter.

So you've been given the whole and you need to work out what one side equals.

So you're going to need to take the perimeter and take the number of sides and divide the perimeter by the number of sides.

So your multiplication facts are going to come in really handy here.

So pause the video and have a go at working out the perimeter for those four shapes.

Well done for having a go at that warmup.

This is a really nice way to get us thinking about perimeter before the rest of the lesson.

So a triangle there has got a perimeter, a whole length all the way around the outside of its three sides of 36.

So we need to do 36 divided by 3.

Hopefully when you hit 36 and three, your mind goes to the 12 times table because 36 divided by 3 is 12.

We then go to square.

So it's 24 divided by 4, which is 6.

You've got a hexagon, which is 72 for its perimeter.

72 divided by 6 is 12.

And then finally, you've got an octagon.

Octagons have eight sides, so 88 divided by 8 is 11.

Really well done if you've got all of those right.

Well done if you had a go.

If it was something that maybe you missed some out or you struggled a little bit with those, do just have another look, because it is a really, it's a nice skill to be able to have to work out the perimeter, to work out the sides from the perimeter, but you can see that your times table knowledge is absolutely crucial.

Let's move on then.

So how would I work out the perimeter of this shape, where we've been given the measurement in metres and centimetres? What do you think you would do if you were given this problem? Well, a really good way of looking at it is to think about partitioning.

So we could start just with our metres.

We've got seven metres along the length at the top there, and we've got three metres in the breadth of the side.

So why have I written seven twice and three twice? Well that's because that rectangle has four sides.

We're only given the measurements of two of them, because opposite sides equal.

So that top measurement is also true for the bottom one, and that side breath is also true for the other side, but we need to make sure when we're adding them up, that we remember rectangles have four sides.

So it's got four sides, where they meet, sorry, two sides where they meet as a seven and two sides where they meet as a three.

So then we add those up and we've got the answer for the metres.

You can add those in whichever order you like, you can do 7 add 7 is 14, add 3 add 3 is 6, which would give you 20, or you could do 7 add 3 and then double it, that's also fine.

Okay, we've done our metres.

We need to not forget that there were also centimetres there.

So we need to add our centimetres as well.

Again, we need to make sure we've got four measurements as there a four sides.

So we've got 5 twice and 12 twice.

Again, however you wish to add those is completely up to you.

I might decide to do 12 times 2 is 24, 5 times 2 is 10.

add those together for 34.

It doesn't matter whichever order you want to do those in.

And as we move through today's lesson, if you can do this working out in your head, wonderful, but there might be times when we get on to larger numbers, that you want to do some column addition or some short multiplication, and that's absolutely fine as well.

However you need to work out the answer is completely up to you.

So final thing we need to do is add those two measurements back together.

The total perimeter of that rectangle is the metres and the centimetres.

So I've got 20 metres and 34 centimetres.

So just to recap, I split up each of the measurements into metres and centimetres and then added them separately and put them back together, making sure I remember that although I've only been given two measurements that represents four sides of my rectangle, and I've got to add four numbers together each time.

Okay, your turn then.

Pause the video and have a go at what I just showed you.

So partition into metres and centimetres, add them together separately, remembering that you should have four of each and then bring them back together for the final answer for the full perimeter.

Well done everybody.

How did you get on? Well, hopefully you started with your metres and that was quite a nice addition or multiplication question if you'd like.

3 add 3 add 1 add 1 should give you 8.

If you've got that answer for your metres, well done.

That's some really good work.

Let's have a look at the centimetres then.

So again, we need those four measurements.

We've got two 21's and two 18's in whichever order you wanted to add those is completely up to you.

I think I would probably end up doing a bit of column addition for those ones just to make sure I've got completely the right answer.

And then we just need to bring those together to give us our final answer eight metres and 78 centimetres.

If you got that one really, really well done.

So here we have partitioned the measurements so that we can give a full answer in metres and centimetres.

As we move on, what if the question said that they wanted the answer given in just one unit, either metres or centimetres? You would need to convert from metres and centimetres into just centimetres.

And to do that, you'd need to think about the relationship between metres and centimetres.

Now, hopefully you remember that metres are the larger measurements, but what's the relationship? How many centimetres are there in a metre? Can you remember? Well, I'll help you if you can't.

One metre is 100 centimetres.

So that's the relationship 1 to 100.

And that means that when we move from one to the other, what we're talking about is timesing or dividing by 100.

So to move from one metre into centimetres, we take 1 and we times it by 100.

We know that multiplication and division are inverse relations, inverse calculations, inverse operations.

So if we're moving from centimetres to metres, we divide by 100.

So 100 centimetres, 100 divided by 100 is 1.

100 centimetres is one metre.

Okay, let's look at that in a slightly different way.

We're looking at our place value columns here.

And that's because it's good to think about when we multiply by 100 we're making something 100 times bigger.

It moves two decimal places to the left.

When we divide, it's getting smaller, it's doing the same thing in the opposite direction.

It moves two decimal places to the right.

If we look at this rectangle, for example, we've been given the measurements in both metres and centimetres.

We need to convert them into just metres and then just centimetres.

If I just go back a moment, if we just look at how I've changed them into metres for three metres and 12 centimetres, I have, I know I've got three full metres, so that's three metres.

12 for my centimetres, and same for two metres and 22 centimetres.

And then all I need to do is times those by 100 to give me the answer in centimetres.

So three metres becomes 300 centimetres, and then I've got 12 centimetres as well.

So 312 centimetres.

Two metres is 200 centimetres and I've got 22 centimetres as well.

I'm going to make that large and let you just look at it for a moment, 'cause that's quite a lot of learning going on there.

Okay, well done.

Time for you to have a go then.

So, oh yeah, and of course we need to add together those final measurements to get the full perimeter of that rectangle.

So lets have a look.

Converting between metres and centimetres, remember that you're timesing, dividing by 100 that is your relationship.

So if we look at that first one, two metres and 34 centimetres becomes 2.

34 metres, two whole metres 0.

34 metres, because the 34 centimetres is not a whole metre.

So it forms the decimal when we're talking about converting it into metres.

And then when we times that number by 100, we get 234.

Let's have a look at working out the next line together.

We've got 5.

7 metres.

So I've got five whole metres and 0.

7 of a metre.

So I've got five metres and 70 centimetres.

What about just in centimetres then? Well, if I times 5.

7 by 100, make it 100 times bigger, move it two decimal places to the left, I get 570.

Have a go at filling in those missing gaps on that grid by yourself.

If you need some help, if you get stuck on one of them, look at the pattern that have been made by the other ones and see if you're also following a similar pattern.

And if you get stuck again, another thing that you can do is think about the number getting two decimal places bigger, two decimal places smaller.

Have a go.

Well done for trying that.

This is something that a lot of people need a lot of practise with and find quite hard.

So well done for having a go.

Let's see how you got on.

So we have eight metres and 23 centimetres is 8.

23 metres, five metres and two centimetres.

Now this is one way you might have made a mistake.

It's not 5.

2 metres, it's 5.

02.

Why do you think that is? Well, because 20 centimetres, that would be 0.

2 of a metre, but we've got the zero in there, because it's just two centimetres.

It's a very small measurement.

It's not into the tens, it's just in the ones.

So when we move into a decimals, that's the column that it goes into and that gives us 502 centimetres.

And then for the last line, nine metres and 67 centimetres is 967 centimetres.

Well done for having a go at those.

Don't worry if you made a few mistakes, this might be quite a lot of new learning for you.

You're taking on a lot today.

So well done.

Okay.

What about this one? Have a go now at using what we just did, which is converting from metres and centimetres into centimetres and have a go at answering this question just in centimetres.

What is the perimeter of this rectangle in centimetres? How did you get on? Well, here's the answer.

So the perimeter in centimetres is 1,528 centimetres.

And there's some working out that you might have done converting those lengths into centimetres.

Really good work everybody.

Okay, your independent task now asks you to record the perimeter of rectangles in different measurements.

So either in metres and centimetres, centimetres only, or metres only.

So pause the video here and have a go at your independent task.

Take as much time as you need, go back over the video if you get stuck and come back when you're ready and we'll talk about your answers.

Really well done.

There's a lot of working out needed here to answer these questions and you're pulling together a lot of your mathematical knowledge.

So well done for having a go.

Let's see how you got on.

Here are the answers.

I'm not going to read them out.

They're there for you to see.

And really well done if you manage to get some of those right.

I'd be very surprised if you got all of them.

If you did, absolutely fantastic.

But if you only got one or two, if you were only feeling confident working out, maybe just in metres or just in centimetres, that's a great start.

So really, really well done for today's work everybody.

Okay, I'd love to see your work, your thoughts and your working out for this perimeter.

If you'd like to, please ask a parent or carer to share your work on Instagram or Facebook or Twitter tagging @OakNational and #LearnwithOak.

But before you go, there is an exit quiz for you just to have a check at how well today's learning's gone in.

Fantastic work today everybody.

Well done and enjoy the rest of your learning today.

Bye-bye.