# Lesson video

In progress...

Hi everybody, I'm Mrs. Crane and welcome to today's lesson.

In today's lesson, we're going to be finding 10, 100 or 1000, less than any given number.

In a moment I'll go through all the equipment that we'll need, so don't worry just yet.

How are you today? I hope you're well and I hope you've got your maths brain switched on.

If you can, can you please turn off any notifications on your phone, so you're not going to get distracted.

Then if possible, find somewhere in home that's nice and quiet and distraction free, ready for today's math lesson.

Okay, then let's go through today's agenda.

So firstly, we'll be using some denies, then we're going to be playing a dice game, then we're going to start looking at some number lines together, and finally, it'll be time for your independent task which will be can you find 10, 100, or 1000 less than any given number, and we'll go through the answers together.

So, if you haven't already for today's lesson, you will need a pencil, some paper and if you've got one, a dice, if you don't have one, you can always ask a parent or a carer, if they could find an interactive version online for you.

Please pause the video now to go and get these things if you haven't got them already.

Welcome back.

So as I said, we're going to be finding 10 100 or 1000 less than a given number.

So we're going to start off with the number 7824.

I've made it using my denies.

You can see here I've got 7000, one, two, three, four, five, six, seven.

I've got eight hundreds, one, two, three, four, five, six, seven, eight.

I've got two tens and I've got four ones.

I've also written it in numbers in this place value grid here.

First thing I'm going to do, is I'm going to subtract 10 from that.

I'm going to take 10 away from that number.

So you can see I've removed one of my tens denies, what number has it left me with? Well done, it has left me with 7814.

I only have one ten here now, not two tens.

So I'm going to put my new number into my answer box.

Now before I go on to subtract 100, I must go back to my original number.

Why is it important that I go back to my original number? Well done.

If I take 100 away from 7814, I'm going to be left with the wrong answer.

So, let's make my answer, my number sorry, the original number there is back to 7824.

Now, this time I'm going to take away 100.

Let's see what happens.

How many hundreds have I been left with? Well done those of you that said you've been left with 700 Mrs. Crane.

So my number is 7724.

And I can put that into my answer box here.

What must I do before I answer my final question? Well done, I must go back to my original number.

Here it is, 7824.

You can see I've made it back to 7824.

Now, this time I'm taking away 1000.

So let's see what happens.

Take away 1000, how many thousands have I been left with? I've been left with 6824.

So my new answer can go in this box here.

Now I've got an always sometimes or never for us to think about today.

So let's say, when I subtract 10, it's the only other digit in the tens column that changes, okay? When I subtract 100, it's only the digit in the hundreds column that changes.

When I subtract 1000, it's only the digit in the thousands column that changes, right.

Let's have a look at an example to see if we can use that to help us decide whether these statements are always sometimes or never true, okay? So my number is 4005.

The first thing I'm going to do, is subtract 10 from it.

Oh, what have you noticed about my tens column? Are there any tens to take away? No, there aren't.

So I'm going to look at my next column.

Are there any hundreds that I can regroup from? No there aren't, that there are four thousands.

So I'm going to regroup one of my thousand to leave me with 3000 to give me 10 hundreds.

Now, I still want to take away 10, can I do that just yet? I can't.

I need to recruit one of my hundreds to give me 10 tens.

I know there are 10 tens in 100, so then, I can take away one of them.

So I'm going to regroup.

One of my hundreds, it's going to become 10 tens.

Now, can I take away 10? Yes, I can.

So I'm going to take away my 10.

And let's have a look at what that new number is going to be.

I now have 3000.

One, two, three, four, five, six, seven, eight, 900.

One, two, three, four, five, six, seven, eight, 95.

So I'm going to put that new number in here.

So it's 3995.

Then my answer can go in here.

Let's think then, when I subtract 10, it's only the digit in the 10s column that changes.

So let's have a look at my original number here.

How many digits have changed between my original number, and the number that I created when I subtracted 10? Well done.

The thousands have changed, the hundreds has changed and so have the tens changed.

So, is my statement always sometimes are never true.

But it's not always true because in the first example we looked at it was only the digit in the tens column.

It must sometimes be true, because we found an example where it is true.

So it's definitely not never true, so answer for this one is sometimes.

Let's have a look then at what happens when we go back to our original number, when we want to subtract 100.

So, here we are back at our original number again, the number was 4005.

This time I'm taking away 100.

Oh no, have I got 100 if I can take away from straightaway? I do.

What do I need to do? Well done to those of you that said, "Mrs. Crane you need to regroup." So I'm going to regroup 1000 leaving me with 3000, the ten hundreds.

Can I now take away one of my hundreds? Yes, I can.

So I'm going to remove one of those hundreds.

Now, what new number have I created? I've created 3000.

One, two, three, four, five, six, seven, eight, nine, 905.

So my face value column here, I need to write 3900.

The zero goes there as a place value to show that there aren't any tens and five ones.

That's my new number in my answer column.

Let's think back to this question then.

When I subtract 100, is only the digit in the hundreds column that changes.

Let's have a look here.

Here was my original number.

Here was my answer when I subtracted 100.

How many digits and which columns have changed? Well done.

The digit in my hundreds column changed, and so, is the digit in my 1000s column.

It's not always true, because in that first example we looked at together, we didn't have to do any regrouping with my thousands column.

But it is sometimes true, because in this example, we did need to regroup.

It's definitely not never true.

Finally then, we're going to look at 4005 subtract 1000.

And considering our last question, I want to take away 1000 are left with 3005.

So I can change that here on my place value grid.

When I subtracted that 1000, only the digit in the thousands column changed.

Let's check.

There was 4005, here's 3005.

Definitely only the digit in the thousands column changed.

Does that mean that always, that's always the case? You have to think.

Can you think of any numbers, but might not be the case? What about if I was looking at a five digit number, I was looking at 10,000 and I wanted to take away 1000.

But not going to look at those digits today.

But if I was looking at 10,005, now I want you to take away 1000 , I'll be left with 9005 which would mean my 10,000 column and my 1000s column would change.

So there are some examples but sometimes this isn't true.

So it's not never again, it's a sometimes we're not going to look at too many of those examples today.

In fact, we're not going to look at any of those examples today.

Right then, now it's time for our let's explore, I'm going to play a dice game.

So, what I'm going to do first is I'm going to explain how we do it.

Then, you're going to have a go at see if you can beat me.

So, we're going to start with a number 1000, that definitely doesn't say, 1000 does it.

That number says, 5000 well done everybody.

Can you begin beet me, to make the lowest number possible.

So, we roll a one, we have to subtract 10, roll a two, we have to subtract 100, we roll three, we have to subtract 1000, we roll a four, we have to subtract 10, we roll a five, we have to subtract 100, and if we roll a six, we have to subtract 1000.

We have five rolls.

So I'm going to show you first, then you're going to play against me.

I roll my dice, I have rolled a one, so I've subtracted 10 to give me 4990.

I've rolled a five, so subtracted 100 to give me 4890.

I've rolled a two, so I've subtracted 100 to give me 4790.

I've rolled one, so I'm subtracting 10 to give me 4780.

And lastly, I rolled a six to give me 3780.

This is the lowest number that I've made, I get five rolls of my dice.

So, what we're going to do now is we're going to play again.

This time, you're going to pause your screen, and you're going to roll five times.

Each time you're going to take off the number that you roll from the grid above and see if you can beat me.

I will go through my five rolls after you've had your go, okay? Remember, we're trying to get the lowest number possible.

Pause the screen now, to have a go at today's let's explore.

Okay, welcome back.

So you're going to play against me and see if your number is lower than my number.

So, I move faster.

I've rolled a six, so my next number is 4000 I've rolled a five, so my number becomes 3900 because I can take away 100.

I've rolled a one, so I'm taking away 10.

So my number is 3890.

I rolled a three, so I'm taking away 1000.

My number is 2890.

Lastly, as well to two, so my number is 2790.

Is your number lower, less than 2790? If it is, well done you've beaten me, if it's not,.

Decide if you won.

Right, let's move on then.

And we're going to have a look today at some function machines.

So, we've got a number here.

The number is 603 and I'm taking away 100.

What numbers going to come out the other side of my function machine? Have a think.

If you never shout at your screen.

503, fantastic.

I've taken away 100 to give me 500.

Now if you're feeling really confident pause the screen now to work out what function is taking place in my function machine.

You're not feeling so confident, don't worry, we're going to look at it together.

So my original number that went into machine, 7040.

The number that came out of machine, 6040.

What happened in my machine? My machine took away 1000.

If you look at the thousands column, 7000 became 6000, so it took away 1000.

Now we're going to have a look at some number lines.

So, here are my numbers on my number line.

I've got 4837, 5837.

What is changing between these two numbers? The thousands column, fantastic.

Firstly, I'm going to work out the numbers that come here, then I'm going to work out the numbers that come here, okay? So, the number in my grid here is 4837.

What number is going to come here if I take away 1000? You see, it's going to give me 3837.

I take away another 1000, well done it's going to give me 2837.

Count with me then it's going to give me 1837.

Oh, what's going to happen if there's no thousands here? My number would be, 837.

There's no thousands left.

Now I'm going to go back from this number up to 5837 before I continue here.

I've got my five thousands here, my eight hundreds here, my three tens here and my seven ones here.

So this time, I'm going this way on my number line.

Am I going back in steps of 1000? Or am I going up in steps of 1000? Well done.

I must be going up in steps of 1000, and if I'm going back this way up the number line.

So I'm going to add another 1000 here, I'm going to have 6837.

I can add one more 1000 here, and I'm going to have 7837.

What I'd like you to do now is if you're feeling really confident, like to have a go at this number line here, look at what's happening between the numbers, and see if you can continue down the number line here.

If you're not feeling so confident, don't worry, we're going to go through it together now.

So to solve this, we're going to use the number line as a representation.

First thing I might want to do is have a look at what I've got already 6353, I know it's dropped to 6253.

The only digit here that's changed is the hundreds column from 300 to 200, which tells me I'm counting down in 100s.

And we're going to fill in the number line by continuing to count down in one hundreds.

So here, I should have 6153.

Here 6053 and it's really important I've got my zero in there as a placeholder, okay? For the next one, I'm going to need to regroup.

So that will take me down to 5953, 5853 , 5753, 5653 and 5553.

Okay, your independent test today is how you make a target number? So, for question one you have got, here you need to use this place value grid.

You can if you want to draw denies on if you don't want to, that's absolutely fine.

Question two is very similar, but the number that you're subtracting from is different.

Question three, you're going to have a go at using a function machine.

Same for question four, you're going to work out what the missing function was.

Question five, you've got a number line, you need to have a go at completing that.

Remember, you can use the tens if you want to, you don't have to.

The same for question six.

Remember what you do, there's a missing number, this side of your number line.

Once you're finished, remember, we'll go through the answers together.

So, press play again on your video.

Okay, welcome back.

Let's go through the answers then.

So for question one, our number is 3021.

If I wanted to take away 10, I get 3011.

If I wanted to take away 100 from 3021, I get 2921.

That's because I need to regroup.

There's nothing in the hundreds column here, so I have to regroup 1000, so it becomes 2000, the 10 hundreds, so it becomes 900.

3021 subtract 1000 then is 2021.

Question two, my number was 4305.

Take away 10, I have to do some regrouping here to get me to 4295.

If I take away 100, I'm left with 4205.

If I take where 1000, I'm left with 3305.

Next I'm going to be looking at function machine.

4897 , 1000 was taken away from it and it gave me 3897.

Question for complete the following function machine.

So we know the number 3402 went into my function machine.

And the number 3392 came back out of it.

What was the missing function? Well done.

It was in fact, 10 was taken away.

We couldn't take away tens, we would have to regroup.

So this would become three hundreds, and this would become 9 tens.

Question five, finish the number line.

So, here's our number line here.

We've got to work backwards here, okay? So we're going to come back, gives us from 4335, 4325, 4315, 4305.

And our last question, we have to work backwards down the number line here.

And then we have to look at this number here.

My number was 3458, my number therefore I'm going up down in steps of hundreds is 3358, 3258, 3158, 3058, 2958.

Then if I look here, remember, this was going down in steps with 100.

So if I want to get from here to here, I must go up in step up 100 to give me 3658.