# Lesson video

In progress...

Hello and welcome to today's lesson.

My name is Mrs. Behan, and today I'm going to teach you how to multiply and divide by 100.

If this is something that you think you can do already, we're going to measure you get even better at it.

And we're going to be looking for the secret of how to multiply and divide by 100.

We're going to look at If that's new to you, you'll find out what that is.

And then we're going to answer some calculations, putting our learning into practise.

So let's take a quick look at the lesson agenda for this lesson.

We are going to practise multiplying by 100.

After that we're going to practise dividing by 100, there will then be a practise activity for you to have a go out followed by an independent task.

And I know you'll be keen to see how you got on.

So I will make sure that I go through the answers with you.

There's just two things you will need to take part in this lesson.

You will need something to write with.

So a pencil or a pen and you'll need something to write on.

So some paper.

If you haven't got those things to hand, just pause the video whilst you go and get them.

Try to make sure that you're working in a quiet place.

So you won't be disturbed in the lesson.

So to get us warmed up, we're going to practise some, skip counting.

The numbers are going to come up on screen and all you have to do is say the number.

Let's go.

100, 200, 300, 400, 500, 600, 700, 800 900 1000.

This time we're going to say the number of hundreds in each number.

So we're going to count like this one, 100 two one hundreds, three one hundreds.

You get the idea.

I'd like you to pay attention as well to the hundred blocks that come up in the corner of the screen.

Let's count.

100, two one hundreds three one hundreds, four one hundreds, five one hundreds, six one hundreds, seven one hundreds, eight one hundreds, nine one hundreds, 10 one hundreds.

And you'll notice that I've put 1000 underneath the number because ten one hundreds is the same as saying 1000.

For the next part of the lesson, we're going to take ourselves to the cinema.

We are going to be the managers of the cinema, and we're going to be looking at how many people visit in the afternoon and how many people visit in the evening.

Do you like going to the cinema? I do, I love getting coffee in that big chair, having a huge book of popcorn and a big fizzy drink.

It's one of the best experiences.

So I'd like to welcome you to Mrs. Behan cinema.

This afternoon, there was one person in the cinema.

This evening there are 100 times as many.

How many people in the cinema this evening? So let's think of one and to make it 100 times the size.

So we're thinking of one and really we are multiplying by 100.

So we have calculated one multiplied by 100, which is equal to 100.

100 is 100 times the size of one.

So 100 people is 100 times as many as one person, there are 100 people in the cinema this evening.

Let's take a different day.

This afternoon there were two people in the cinema.

This evening there are 100 times as many.

How many people are in the cinema this evening.

Let's think of two and make it 100 times the size.

So we're thinking of two are multiplying and get by 100, two multiplied by 100 is equal to 200.

200 is 100 times the size of two.

200 people is 100 times as many as two people.

So there are 200 people in the cinema this evening, Much, much busier than in the afternoon.

This afternoon, there were three people in this cinema.

This evening there are 100 times as many.

How many people in this cinema this evening? I'm sure you've worked this out by now.

Let's think of three and make it 100 times the size.

So we are thinking of three and multiplying it by 100, three multiplied by 100 is equal to, can you tell me? That's right 300, 300 is 100 times the size of three.

So 300 people is 100 times as many as three people.

There are 300 people in the cinema this evening.

So by opening our cinema, we have learnt that to find 100 times as many, we multiply by 100.

So here are the calculations that we've looked at so far.

Can you say that with me? One multiplied by 100 is equal to 100, two multiplied by 100 is equal to 200.

Three multiplied by 100 is equal to 300.

Did you notice anything about the products? I hope you note that they are all multiples of 100.

And what do all of these products have in common? All of these multiples of 100 have in common.

They've got zeros in the tens place and zeros in the ones place that's for all of the multiples of 100, let's look at number 300 here.

What is the value of this? Three, well we know that means three hundreds.

What's the value of this zero.

That's the tens place.

So that means zero tens.

And this zero here, it means zero ones because there's zero is in the one's place as a place holder.

Well done everyone.

So let's read the words on the screen to summarise what we have noticed so far.

All multiples of 100, have both a tens and ones digits of zero.

Let's say it again to make sure it's sticking domains.

All multiples of 100, have both a tens and ones digit of zero.

I'm interested to see whether you can sort these numbers into the table.

Think carefully about how we can tell a multiple of 100 apart from a number that is not a multiple of 100.

Pause here whilst you have a go, how did you get on? Was it easy or was it tricky? Did you remember that multiples of 100 have a zero in the tens place and the ones place that should have helped you? Okay let's sort the numbers into the table.

700 is a multiple of 100 because it has a zero in the tens and the ones place.

300 is a multiple of 100, 601 is not a multiple of 100.

This is because there is a one in the ones place.

150 is not a multiple of 100 either.

I hope that one didn't trick you.

There is a zero in the ones place, but we have five tens in this number.

So we know it is not a multiple of 100, 400 is a multiple of 100, 4,001 is not multiple of 100 again, because there is a one in the ones place.

This is the tens place.

This is the hundredths place.

So don't be tricked by the two zeros in a number.

It's not a multiple of 100, because it has a one in the ones place 610 is not multiple of 100 either.

We are now going to systematically work through some calculations using a to help us.

If you show what the word systematically means.

It just means we're going to go through in a certain order to help make the calculations easier for us.

Okay, so we're now going to look at the relationship between multiples of 100 and other numbers on the.

This here is a chart.

As you can see the value of the numbers increase as they go up the charts, or if you start at the top and work down the values decrease, they get smaller.

Up here at the top are some sentence stems that I'm going to be using.

And I would love it.

If you could join in with me, we've got blank multiplied by 100 is equal to blank.

And then we're going to reverse it by saying blank is 100 times the size of blank.

I'll start our first and join in when you can.

One multiplied by 100 is equal to hundred.

100 is 100 times the size of one.

Two multiplied by 100 is equal to 200, 200 is 100 times the size of two.

Three multiplied by 100 is equal to 300, 300 is 100 times the size of three, four multiplied by 100 is equal to 400, four hundred is one hundred times the size of four.

Five multiplied by 100 is equal to 500, 500 is 100 times the size of five.

Six multiplied by 100 is equal to 600, 600 is 100 times the size of six.

Seven multiplied by 100 is equal to 700, 700 is 100 times the size of seven.

Eight multiplied by 100 is equal to 800, 800 is 100 times the size of eight.

Nine multiplied by 100 is equal to 900, 900 is 100 times the size of nine.

So we can generalise now that when a number is multiplied by 100, the product is a multiple of 100.

I'm sure by now that you've started to see a pattern, perhaps that we can place two zeros after the final digit of the number.

Let's see if it works the same when we use place value counters.

So here is a counter in the ones place.

If we move the counter or this could be a digit two places to the left, the value of that digit becomes 100 times the size.

So here we see number one, when it is moved to places to the left, it's a hundred times the size.

So now it has a value of 100.

So even though we see a one, this one actually represents 100, So let's try it with number six.

Here we're going to look at six and make it 100 times the size.

So step one, we make it 100 times the size and we write in the six in the hundreds place.

And we add in our two zeros in the tens and ones places as placeholders.

So six multiplied by 100 is equal to 600.

So you will notice that all multiples of 100 have a tens and ones digit of zero.

See the words on screen with me now.

To multiply a whole number by 100, place two zeros after the final digit of that number.

Let's say that again, to multiply a whole number by 100 place two zeros after the final digit of that number.

Here's our chart.

Let's look at the ones in relation to the one hundreds and there we can see our zeroes in the tens and the ones places let's go back to Mrs. Behan's cinema this time going to look at the people who come in the evening and compare it to the people who were in the cinema this afternoon.

So this evening, there are 100 people in the cinema, 100 times as many as this afternoon.

So how many were in the cinema this afternoon? So one multiplied by 100 is equal to 100, 100 divided by 100 is equal to one.

100 is 100 times the size of one.

So there was one person in the cinema.

Let's take a different day.

This evening there are 200 people in the cinema.

100 times as many as this afternoon, how many were in the cinema this afternoon? Well, we know that two multiplied by 100 is equal to 200.

200 divided by 100 is equal to two.

200 is 100 times the size of two.

There were two people in the cinema.

This evening there are 300 people in the cinema.

100 times as many as this afternoon, how many were in the cinema this afternoon? I think you'd be able to work this one out now.

Three multiplied by 100 is equal to 300, 300 divided by 100 is equal to three.

300 is 100 times the size of three.

There were three people in the cinema and I'm sure by now you're starting to see the special relationship between multiplication and division.

Division is the opposite operation to multiplication.

We call this the inverse operation.

See the words on the screen with me.

To find the inverse of 100 times as many divide by 100.

Let's say that's again.

To find the inverse of 100 times as many divide by 100.

We're now going to look at some more calculations using the chart.

Can you remember what systematically means? We're working systematically it means we're going to work through a fixed plan or method.

As we look at the relationships we're going to use our sentence stems from earlier.

Blank multiplied by 100 is equal to blank.

Blank is 100 times the size of blank.

Our new sentence is blank divided by 100 is equal to blank.

One multiplied by 100 is equal to 100.

100 is 100 times the size of one.

100 divided by 100 is equal to one.

Two multiplied by 100 is equal to 200 and 200 is 100 times the size of two, 200 divided by 100 is equal to two.

Three multiplied by 100 is equal to 300 and 300 is 100 times the size of three.

300 divided by 100 is equal to three, Four multiply it by 100 is equal to 400 or 400 is 100 times the size of four, 400 divided by 100 is equal to four, Five multiplied by 100 is equal to 500 and 500 is 100 times the size of five, 500 divided by 100 is equal to five.

Six multiplied by 100 is equal to 600 and 600 is 100 times the size of six.

600 divided by 100 is equal to six.

Seven multiply by 100 is equal to 700 and 700 is 100 times the size of seven.

700 divided by 100 is equal to seven.

Eight multiplied by 100 is equal to 800 and 800 is 100 times the size of eight.

800 divided by 100 is equal to eight.

Nine multiplied by 100 is equal to 900 and 900 is 100 times the size of nine.

900 divided by 100 is equal to nine.

Have you noticed that all of the numbers in the hundreds row are multiples of 100 and all of the dividends in the division equations are multiples of 100 as well.

So did you notice any patterns when we divide it by 100? Did you notice anything to do with the zeros? We removed two zeros from the tens and ones places.

So we can generalise that to divide a multiple of 100 by 100, we can remove two zeros from the tens and ones places.

Say the words on the screen with me.

To divide a multiple of 100 by 100, remove two zeros from the tens and ones places.

Have a go at complete in the missing numbers in these calculations, using what you've learned in this lesson.

I want to know is the answer a multiple of 100.

You just need to write down true or false.

Once you've finished, come back to me and we will go through the answers together.

Okay, how did you get on.

I'm sure you did a fantastic job.

60 multiplied by 10 is equal to 600, 600 divided by 10 is equal to 60.

600 divided by 100 is equal to six.

400 divided by 10 is equal to 40.

90 divided by 10 is equal to nine.

720 is equal to 72 multiplied by 10.

You can see in this activity, I was asking you to practise your multiplying and dividing by 100.

50 is equal to 500 divided by 10.

800 divided by 100 is equal to eight.

40 is equal to 400 divided by 10.

27 multiplied by 100 is 2,700.

2,700 divided by 100 is equal to 27.

270 is equal to 10 multiplied by 27.

Those are some tricky questions, but I knew you'd be up for the challenge.

Here are the answers to our true or false.

Two multiplied by 100 would give the product of 200.

So that is a multiple of 100.

So it's true.

500 divided by 100 would leave us with five.

So that is not a multiple of 100.

12 multiplied by 100 would give us 1,200.

So it would be a multiple of 100.

900 divided by 100 would be nine.

So that is not a multiple of 100.

And 25 multiply by 100 would give us a product of 2,500.

So that would be a multiple of 100.

There were some tricky questions in there, but I know you've got a really good understanding of place value.