Lesson video

Hello everybody.

My name's Miss Brinkworth.

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

Let's look at the learning objectives together.

What we're going to be doing is calculating the perimeter of composite shapes.

We'll look at that learning objective in a bit more detail and pull apart those words and what they mean.

So if we look at today's lesson agenda, what we're doing is we're going to look at what we mean by composite shapes.

We're going to think about how we find missing values of composite shapes.

That's one of the key learnings for today.

And then there'll be an independent task where you'll have a chance to apply what you've learned.

You will need a pencil, a ruler, and some paper.

A rule is not absolutely crucial.

If you can't find one at home, please don't worry.

But please make sure you have got pencil and paper.

Take your time to get your equipment now.

Welcome back.

Hopefully you've got everything you need.

So let's get started.

Okay, how would we work out the perimeter of this shape? We know how to work out the perimeter of rectangles and squares as we can take each size, add it together.

And then we'll have worked out the whole perimeter.

Remembering that the perimeter is the distance all the way round the outside of a shape which means we need to add together all of the sides of the shape.

Can you see any problem with adding together the sides of the shape? Well, we've got a missing value as we go round the shape.

And what I like to sometimes do is put my finger or my pen on it.

And if you take a pen, you can draw a line and you can say right, I've added up that side and that side and that side and that side.

Oh, there's a side here where I haven't been given the value.

How do we work out that value when we haven't been given it? Well, we've been given clues and we've been given everything we need to work out the value of that side.

We just need to have a good look.

So if you look here at that second picture what we're showing is that, you know the long side down the left-hand side of it is 10 and the short side there at the end is 4.

So when we're comparing sides, we make sure we're either looking at the vertical lines or horizontal lines.

So if that side is 10 and that one is 4, we can do 10 takeaway 4 to give us the missing side, which must be 6.

So if we've got our side which is 6 and our side which is 4, they add up and then we know that, that will be the same as the 10.

That side is six.

How about here? We have two missing sides.

See if you can use the information you've been given.

I promise you that there is everything you need that to work out what those missing sides are.

How did you get Tom? So if we look at the shape, again we've got the 10 on the side.

So how are we going to use that to help us with that missing vertical side? we've got one vertical, which is 10.

The long one is 10.

And then another vertical is 5.

So that missing vertical must be 5 cause we need to 5 and 5 is 10.

10 is 5 takeaway.

5 is our answer when we do the 10 takeaway the 5, the missing one must be 5.

What about the other missing one? This one, this time is a horizontal.

So we look at our horizontal lines that we've been given to help us.

The long horizontal line at the bottom tells us 11.

And the one at the top is 4.

So if we're trying to get from 4 to 11, we can do 11 takeaway 4 Which will again, give us 7.

Well then if you worked this out, if you didn't, let me just explain to you one more time, what I've done.

So to work out that 5, it's a vertical line on this shape.

So I'm going to look at the other vertical lines that I've been given.

The long one down this side is 10 and the shorter one there is 5.

So those are my two verticals that I've been given.

I know with shapes like this, that we must have the same.

So I'm going to take my 10.

I'm going to take away the 5 that I've been given because what's missing is going to add up to 10.

So 5 and 5 gives me 10.

Then for my horizontals, I'm working out that missing horizontal there.

I've got 11 at the bottom.

11 takeaway 4 will give me what that missing horizontal line is.

So 11 takeaway 4 is 7.

Okay, what about one like this, where there a lots of missing values? Can look a bit overwhelming but what's important to do is just take each one at a time and think carefully about how to work it out.

Think about whether they are vertical.

So they're going up and down or if they're horizontal they're going across.

And then you'll look for the other values which are vertical or horizontal to help you work them out.

So for example, with this one, how did I know that this one was 3? This missing calculation, this missing side is 3.

How do I know that? Well, if I put any other one as well, hopefully you can see that it's three because it's the same as the one opposite there.

The shape is symmetrical.

So if that's vertical side there was 3, that vertical side will be 3.

Same with my missing 10 on the other side is exactly the same side as the one that I've already been given, which is 10.

So I'm going to put those ones in first, before I try and miss out to try and work out that missing one in the middle.

Because then I've got all of my ones.

And so I can have a go at working out what the middle one is.

To work out what the middle one is, it's a horizontal.

So the long horizontal at the bottom which is all of them added together.

All of those different horizontals added together to make 24.

I've been given 4 and 4.

So if I do 24 takeaway 4 and take away 4, it will give me my missing line, which is 16.

Okay, your turn.

Here's another chance for you to have a go at finding some missing lines, some missing lengths of lines.

The one on the left that you are looking for the whole this time.

So there's a long vertical, which is missing.

So you're looking for the whole.

Think about which parts add together to make that whole to give you the long vertical.

The horizontal at the top is a part.

So you can take away some values to find that one at the top.

Have a go.

How did you get Tom? Now please, don't worry too much if you're finding this hard This is a tricky thing to learn especially when we're doing it over a video.

So please, don't worry if you're finding this a bit tricky.

Listen carefully to how I've worked it out and see how you get on with your independent task in just a moment.

So if we take that vertical first, like I mentioned, it's the whole, it's the longest side on that shape.

So I need to add together the other vertical lines that will give me my answer.

So I've got a vertical which is 4 and another vertical which is 4.

So if I add those verticals together that will give me my answer there, which is eight.

How then did I work out this three? How did I work out that, that one at the top is three? Well, this was a part this time.

It's a shorter side.

So I'm working out a part.

I've got 10 along the bottom as a long horizontal.

I've also got 7 there as well.

So if I take 7 away from 10, what I'm left with must be my last horizontal.

So 10 take away 7 is 3.

So you need to look really carefully at these shapes.

You need to think about what you know about shapes like this.

They are made up of rectangles.

And so they follow the same rules as rectangles.

That means the opposite sides are equal.

And so we can use those to add or take away to find out those missing sides.

Okay, time now to pause the video and have a go at your independent task.

Take as long as you need.

And if you're finding you're stuck, come back and have a look at.

rewind the video and have a look at how we worked out the missing sides together.

Come back together when you're ready for the answers.

Really well done for having a go at these at home everybody.

I'm going to give you the answers here.

So if you just worked out the missing side that's absolutely fine.

And if you managed to find just a few of them, you really are doing brilliantly well.

So what I'm going to do is just put them up for a moment for you to have a look.

So the missing sides have mainly been put in, in purple or green, there's some of them are in green and the perimeter, where we've added together all of the sides has been given to you in pink.

So have a look at how you go Tom.

Well done, if we just talk about a couple of them, I'm not going to go into detail about all of them 'cause I think you could probably get a bit bored of my voice.

But if we look at one and we could see that one of the missing sides which is 9 cm is a whole, it's a long side.

So you needed to add together your other two vertical values to find that out.

Well, then if you could say that your vertical values were 7 and 2.

So that gave you that long, that whole side, which is 9.

You're missing one at the top.

If you could say that you had horizontals of 8 and 5 and that's your missing parts, the whole was 8, you had a part which was 5.

So the missing part must be 3.

Well done.

If you managed to get some of those rights it really is quite a lot to pull together there.

You're having to use lots of different mathematical skills.

It's about knowledge of rectangles and then looking carefully to see whether you need to add or subtract to find a part or a whole that's missing.

Really well done for working so hard today everybody.

Okay, I'd love to see your working out for today.

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

Okay, that's the end of today's lesson.

Great work, everybody.

Please enjoy the rest of your learning today.

Bye bye.