Lesson video

Hello, everyone.

I'm Miss Brinkworth.

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

If you look at our learning objective.

What we're going to be learning today, is calculate and compare area of rectangles using square centimetres.

So we're going to be looking at rectangles in detail, how to work out that area quick and effectively, and how we do that using squared centimetres, as our measurement today.

So if we look at our agenda for today's lesson, what we're doing is we are going to be estimating, to begin with.

So just like when we're doing multiplication or adding questions, an estimate is a really good way of making sure that we're onto the right track.

So we're going to think about how we can estimate today, when we're looking at area.

we're then going to accurately calculate.

So estimations are great, but there are times that we need, to accurately work out the exact area.

So we're going to find a really clear formula, but accurately calculating area today.

Then of course, there'll be a chance for you to apply that independently.

So take your time and apply your new learning to your independent tasks.

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

Just a little bit of fun, a few questions for you to work out, how well today's learning's gone in.

So all you're going to need is a pen or pencils and paper, and a ruler would be useful, but we understand that you are at home, Maybe you don't have a ruler.

Don't worry if you can't find one, but do pause the video here and get your equipment together? Welcome back, hopefully you've got everything you need.

Let's get started.

So have a look at these three rectangles.

I wonder if you can have a go at estimating the area.

So what you're going to be measuring them in, is those squares that you can see around the outside.

I wonder if you can estimate, what you think the area of each is, and think about which one do you think has got the biggest area? which one do you think has got the smallest area? So pause the video here and have a go.

Now this can be quite a tricky thing to do, but it's important to look and think about, which one you think is bigger, which is smaller.

And then when you do get some accurate answers, you can kind of check with you whether they sound right.

So, the one on the left is actually the largest.

The one in the middle is the middle.

And the one on the right is the smallest.

I wonder if you got that right? In terms of your estimating, which is larger, which is smaller.

but it also, if you got it wrong, hopefully that shows you that estimating, when it comes to area can be quite tricky.

It's almost just a sort of hassle, or what does it look like type situation.

So it just shows that it's really useful to be able to accurately say what the area of a shape is.

So just remember that when we're talking about area, we're talking about the space that the surface takes up.

So it's not a measurement from one point to another, it's a measurement of the whole surface of something.

So, if I was to measure the surface of my book, it would be all of this would be the area of my book.

If you were talking about the area of your room, it would be the whole space at the floor takes up.

So let's move on and have a think about, how we can measure that really accurately.

If you look at this rectangle, we are being told the measurements for two sides.

We're being told that the length is 10, and I'm sure we have a breadth of six.

Why are we only being given two sides? Well, on a rectangle, we know that the other sides of the same, but actually with area, we only need those two sides.

That's because when we work out the area, of a rectangle or a square, all we need to do is times one side by another.

So as long as we're timesing length by breadth, just meaning if there are lengths, if there are sides which are different lengths, you are timesing those together.

So it wouldn't work.

If we decided two times together, 10 and 10, for example, that wouldn't give us the right area.

The correct area will be two times, the two lengths which are different, obviously with a square, they're all the same.

So you would times together the same number.

So for this one, we got 10 and six.

So do work out the area of this rectangle? It is as simple as timesing 10 by six.

Now the length of each side has been given to us in centimetres.

And so when we wake up the area, it's not a simple centimetre measurement anymore, but its centimetre squared.

Remember that little two, tells us that we're talking about a two D shape, the area that a two D shape takes up.

So we find our length and our breath, 10 and six, we multiply them together and then we have our area.

So when I mentioned a formula earlier, what that means is where you have a rule, which you can apply to any shape.

So for example, rectangles, the formula for working out area, is length multiplied by width.

You can apply that to any rectangle.

As long as you can work out the length and width, all you need to do is multiply them together, and you will have found the accurate area.

So your turn, how a go with these shapes, thinking about what we area is be careful, they're not all centimetres.

So they won't all be centimetre squared, pause the video and take as long as you need, to work out the area the shapes.

Well done, everybody you're working really hard at working out the area today.

So if we look at that green rectangle, we've got nine and four, nine times by four, or if you would prefer four times by nine, whichever times table you feel most comfortable with, we know that multiplication can be done in any order.

So nine times four or four times nine, going on nines, nine 18, 27, 36, 36 centimetres squared.

What about the next one? Then this grey shape, 12 times three or three times 12 will give us 36, but I made sure looking at how the sites have been measured.

They are in millimetres this time.

So my area measurement has to be millimetres squared with that little two just above the millimetres.

Let's have a look at the other ones then, why on that blue shape? How can we work out, when they've only given us one side? Why do you think on that shape? They only gave us one side.

They've only given us one side measurement, because it is a square.

What do we know about squares? All four sides are the same.

So we know that all of the sides are six.

And so we just do six times six, to work out that one which is 36, but we still look carefully at the unit of measurement that's been used it's centimetres.

So for my area is centimetre squared.

When you see a question like that, and you think hang on a minute, there's some information missing.

I can't do it.

Try going back again and having another look, because they will have given you, all the information you need.

So try and think about another way of looking at it.

Why might they have only given us one measurement? it's because it's a square.

And finally we have this dark blue shape, which reduce six times seven is 42, but I've made a mistake here.

Can you see what it is? The measurements for each side, were not given to me in centimetres.

They were in metres.

And so my area measurement should be metres squared, not centimetre squared.

Really well done if you got all of those right.

So just to a recap, what we're doing when we find the area of rectangles, is we are multiplying the length and the width.

We know that squares are types of rectangles.

So the same rule applies, but because squares have sides all the same length, we might just be given one side, and we just times that by itself, to find the area of a square.

It's time for independent task here.

It's all the same thing that we've been looking at, in terms of multiplying length by width, to find the area of rectangles.

Thankfully they're all in centimetre squared.

So you don't need to worry about getting your unit measurement correct.

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

Come back through your answers when you're ready.

Well done for trying so hard with your independent task everybody, let's see how you got on.

Don't worry if you've made some mistakes, these are quite tricky to work out.

And you're looking at new learning here.

But if you have made a mistake, think about where that mistake has come in.

Has it come in? Because you've got the wrong idea about, how to work out area? well remember you need to times one side by the other, is it because you've not quite as comfortable with your times tables.

And so that's, what's letting you down.

So if we look at that purple square, purple rectangle, sorry, we've got nine times seven or seven times nine, whichever way round you want to look at that, You get the answer as 63.

I think about seven times nine as just seven less than 70.

I know that 10 times seven is 70.

So nine times seven is just seven less.

That's how I remember that fact.

You've got 20 times 30 for that pink rectangle.

So you kind of have to do quite a lot with that one, two times three is six, 20 times three would have been 60.

And so 20 times 30 is 600, really well done If you've got that one right.

The green one is a square.

So we know we do six times six.

Oh no, sorry.

My apologies.

It's not a square.

It's still a rectangle because one is five and one is six.

So it's five times six is 30.

Your green one.

You've got eight times 12 So 96 for your blue, 10 times 25, not too simple a question really, 25 made 10 times bigger moved one decimal place, moved left one place value column 25 turns into 250.

And then 15 times two is thirty.

Maybe you need to do a bit of column addition to work that out 15 at 15 would give you the right answer.

But 15 times two is 30 in a really great fact, to just learn and be quite confident with, because then it will help you, with lots of other calculations.

So you could practise 15 times two is 30.

If that's not when you feel too confident with.

I'd love to see your working out today.

I'd love to see how you, worked out that the area of those rectangles.

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

But before you go, please have a grow at the exit quiz.

There's just a few questions on there, to really practise what you've learned today, In this lesson.

You've worked incredibly hard, working out the error of rectangles today.

I'm really pleased with all of your hard work well done.

Enjoy the rest of your learning of your day.

Goodbye.