Lesson video

Hello, my name's Mrs. Cornwell, and I'm going to be helping you with your learning today.

I'm so pleased we're working together.

I know you'll work really hard and I think we're going to do brilliantly.

So let's get started.

So today's lesson is called Finding Missing Numbers Between 20 and 100, and it comes from the unit patterns in counting from 20 to 100.

So we're going to look at different ways, different strategies that we can use to help ourselves with new learning.

So we can use things that we already know to help us to find out new things.

And we're going to hopefully, by the end of today's lesson, feel much more confident with doing that.

So our keywords, the words that will be important for us today are after, my turn after your turn.

And before, my turn before your turn.

Between, my turn between your turn.

And strategy, my turn strategy, your turn.

Well done.

So in the first part of today's lesson, we're going to find missing numbers within a decade, okay? Just within one decade.

And then in the next part of the lesson, we'll go on and we'll find missing numbers on number tracks, and we'll be able to position them as well.

And that might be looking at more than one decade.

So here's Aisha and Lucas.

Aisha is hiding numbers on the number track for Lucas to find.

Can you help her work out the missing number? So we can see that a number's being covered up there, can't we? She says you can look at the other numbers to help you.

And Lucas says, I will count along from the start of the number track to find it.

21, 22, 23, 24, 25, 26.

So he went back to the beginning of the number track, didn't he? When finding missing numbers, you don't have to go back to count from the start of the number track to help you find the number.

Lucas is saying, I wonder if I can use the other numbers to help me find the missing number.

So you might be able to use some of the other numbers there without counting them all.

Aisha says, I have a quicker away.

The number after five is six.

So tap out five, then six on the Gattegno chart.

So there's five and then there's six.

Now tap out 25 and 26.

There's 25 and 26.

What do you notice? There's Lucas.

He's noticed that.

He says, I know that the number after five is six, so I know the number after 25 is 26.

So he's used that pattern to help him.

The missing number must be 26, therefore.

Find the number after 22.

So there's another number track there that could help us.

We could think about those patterns.

I know the number after two is three, so I know the number after 22 is 23.

That's right.

So now it's time to check your understanding.

So it says find the number after 27, and there's a stem sentence there to help us.

Either know the number after seven is eight.

So I know the number after 27 is mm? So pause the video while you have a think about that.

Okay, so what did we think then? I know the number after seven is eight, so I know the number after 27 is 28.

That's right.

You can use the patterns within the decades to help you work with larger numbers.

So I know that the number after seven is eight.

I know the number after 27 then is 28.

I know the number after mm is mm, what will it be? I know the number after 37, that's right, is 38.

We used those patterns to help us, didn't we? Aisha's saying, I wonder what the number after 47 would be.

Or 57.

So it would follow the same pattern, wouldn't it? Perhaps you could think of some other numbers that would follow that pattern as well.

So, time to check your understanding again.

So, find the missing number.

So we've got two number tracks there, haven't we? And you are going to use the stem sentence to explain how you know.

So I know the number after mm is mm, so I know that the number after mm is mm.

So pause the video while you have a try at that.

So, let's see then.

I know the number after seven is eight, so I know the number after 47 is 48.

That's right.

Excellent.

Some of the numbers have been taken off this number track.

Lucas is saying, I wonder how I will find the missing number now.

Aisha has an idea.

She says, I will count backwards.

29, 28, 27, 26, 25, 24.

Lucas has found a quicker way to find the number.

I'll use the patterns in numbers to help me, he says.

I know that the number before two is one, so I know that the number before 22 is 21.

That's right.

Look at the number tracks and use them to help complete the stem sentences.

I know that the number before five is four, so I know the number before mm is mm.

That's right, I know the number before 25 is 24.

Look at the number tracks again and complete the stem sentences.

So we've got, I know the number before mm is mm.

That's right, I know the number before eight is seven.

So I know the number before 28 is 27.

Lucas says, I wonder what the number before 38 would be? Or 48? Perhaps you could use the patterns to help you find that out.

So time to check your understanding again now.

Use the number tracks to help you complete the stem sentences.

I know the number before mm is mm.

So I know the number before mm is mm.

So pause the video now while you try that.

Okay, so let's see what we found out from that then.

I know the number before five is four, so I know the number before 25 is 24.

Excellent.

So your task for the first part of today's lesson then is here.

So it says write the missing numbers to go on the number track and explain to your partner how you worked it out.

Okay, so you can see you've got some number tracks, some have got the numbers missing at the end, some have got the numbers missing at the beginning.

And it says use these words to help you, before, after, and between.

So when you're explaining to your partner how you worked it out, you can explain if you were thinking about the numbers before or after or in between, can't you? So pause the video now while you try that.

So let's see how we got on with that.

Okay, so you may have counted all the way along the number track forwards or backwards to help you.

That will be one strategy, one method you could use.

But you could also just use the number next to it, couldn't you? So on this first track you could think, I know the number after eight is nine, so I know the number after 28 is 29.

And again, I know the number after eight is nine.

So I know the number after 38 is 39.

That's right.

And then this next set is a little bit more tricky because it follows the decade numbers, doesn't it? So, but we know that after zero, the number that comes after zero is one.

So we know it's going to end in a one.

So we'll have 30 and then 31.

And again, 40 and 41.

Now this next set has the number before missing, doesn't it? So we can look at 26 and think, right, I know the number before six is five.

So I know the number before 26 is 25.

And I know the number before 36 is 35.

That's right.

Okay, and then this one below down here.

So we are looking for the number before 29, aren't we? I know the number before nine is eight.

So I know the number before 29 is 28.

And I know the number before 39 is 38.

That's right.

Now these tracks over the last set here, they have some missing numbers in between other numbers, don't they? You could think about the number that's in between, but you could also use, you could think, I'm going to think about the number that comes before or the number that comes after.

So for example, you might look at that one and think, I know the number after four is five, so I know the number after 24 is 25.

Or you might have thought, I know the number before six is five.

So I know the number before 26 is 25.

So there's two different strategies you could use there, aren't there? Okay, and then for this next one, I think I'm going to use the after.

So I know that the number after seven is eight, so I know the number after 27 is 28.

But you could have looked at the 29 to help you as well.

And this next set, I think I'll look at the 29 to help me with both numbers there.

So I think I'll think the number before nine is eight.

So the number before 29 is 28.

I know the number after nine is 10, so we'll make a new 10.

So after 29 it will be a new 10, it will be 30, won't it? That's right.

Okay, and then this one down here, I think I'll use the number after again.

So I know the number after eight is nine, so I know the number after 28 is 29.

And then here I think I'll use the before.

So I can see 32.

I know the number before two is one.

I know the number before 32 is 31.

Well done.

That's excellent, you've used your patterns that you've spotted there and what you already know to help you learn some new facts.

That's excellent.

So the next part of today's lesson is about finding and positioning missing numbers on number tracks.

So Lucas and Aisha find a longer number track and hide a number on that.

Okay, you can see it there, can't you? And you can see what there's a number missing.

What do you know that can help you to find it out? So Lucas says, "I will mark on my decade numbers "to help me see the decades." That could be helpful, couldn't it? He's put on 20 and 30 and 40.

Aisha says, "Now we can see the number is between 20 and 30, "so we know it must be in the 20s." What numbers are between 20 and 30? So Aisha's saying this is a 20s decade.

All of the numbers start with 20, or two 10s, and we can see them all there, can't we? So it goes from 21 to 29.

So find the missing number, then.

What is the missing number? We know it's in the 20s, don't we? But let's look at the numbers that we've got there before and after it to help us find out exactly which number it is.

So, I know that number after mm is mm.

Okay, so we're thinking about what each number is after, and we can use the end of the numbers, the one, two, three, four, five, six, seven, eight, nine to help us, can't we? So I know the number after seven is eight, so I know the number after 27 is 28.

We can also think about which number it comes before.

So the number before, so we know the number before nine is eight.

So the number for before 29 is 28.

And we can also think about what what it's between.

So, 28 is between 27 and 29, isn't it? That's right.

So we found the missing number.

What numbers are before between 20 and 30 then? So this is the 20 decade.

All the numbers start with 20 or two 10, all of the ones between 20 and 30.

What numbers are between 30 and 40? This is a 30s decade.

All the numbers start with 30 or three 10s.

Lucas and Aisha find another number to hide.

You know it's between 30 and 40, so it must be in the 30s.

You know that it is the number after 30.

So it must be 31.

Lucas takes some numbers off the number track.

So now there's a lot of numbers missing, aren't there? Aisha says, "I wonder how I can find "the missing numbers now?" You can use the decade numbers to help you, can't you? And you can use the other numbers that are left to help you as well.

So Lucas looks at the decade numbers and he says, "I know it's in the 30s "because it's between 30 and 40.

"I can see 34." So he is going to use 34 to help him.

"I will count on.

"I will start at 34 and I count on, 35, 36." So he thinks it's 36.

Aisha says she spotted a different way.

I wonder what Aisha's going to do.

So what do you know about the missing number? "It's in the 30s, it's the number before 37", Aisha says.

Oh, so she used a different number to help her.

I know that the number before seven is six.

So I know the number before 37 is 36.

So Lucas counted forwards to find it, didn't he? And Aisha found it counted backwards.

Time to check your understanding now.

So complete the stem sentences to help you find the missing number.

Okay, so you can say it is in the mm.

It is the number before mm.

I know that the number before mm is mm, so I know that the number before mm is mm.

So, pause the video while you have a try at each part of those stem sentences there.

Okay, so let's have a think then.

So we can see it's between 20 and 30.

So it is in the 20s.

It is the number before 23.

I know that the number before three is two.

So I know the number before 23 is 22.

Well done.

We can also use the decade numbers to help us see the number patterns more clearly.

So look for the pattern, then use the stem sentence to help you explain.

The number after 20 is, so the number after 30 is.

The number after 20 is 21, so the number after 30 must be 31.

Because it follows the same pattern, doesn't it? Well done.

So now, time to check your understanding again.

So use the pattern to help you find the missing number and use the stem sentences to help you explain.

So the number after 25 is mm.

So the number after 35 is mm.

Okay, so pause the video while you have a try at that.

Okay, so how did we do? Let's have a look.

So, the number after 25 is 26.

We can see, can't we? So the number after 35 must be 36.

That's right, well done.

Aisha tries to make the game harder by hiding more numbers.

You can see she's hidden three numbers there, hasn't she? What strategies could you use to find the missing numbers, I wonder? You could count forwards from 27, couldn't you? You could say 27, 28, 29, 30, 31, 32.

I wonder if there's another way you could do it.

Hmm.

That's right, you could count forwards from 29, couldn't you? You could say 29, 30, 31, 32.

Yeah, well done.

Lucas says he could find the missing numbers by counting backwards.

Is he right, do you think? Could you count backwards to find those numbers? That's right, he could count backwards from 36, couldn't he? He could say 36, 35, 34, 33, 32, 31, 30.

Could he find a different way? Could he count backwards from a different number? That's right, he could count backwards from 33, couldn't he? He could say 33, 32, 31, 30.

So lots of different strategies to find those missing numbers there.

Time to check your understanding again.

So you're going to find the missing numbers here and then explain how you found out.

So think about which strategy you would like to use, and you might check it using a different strategy.

So pause the video now while you have a try.

Okay, so let's see what you did.

So you may have counted forwards from 34.

You might have gone 34, 35, 36, 37, 38, 39.

Or you may have counted forwards from 36.

You might have gone 36, 37, 38, 39.

You may have also counted backwards.

You could have said 43, 42, 41, 40, 39, 38, 37.

Or you may have counted backwards from 40.

You may have gone 40, 39, 38, 37.

Well done.

The children try to find the missing number on this number track here.

So I wonder what clues could help us there.

Aisha says, "I know it is between 30 and 40, "so it must be in the 30s.

"I will start at 30 and count on." Lucas has a different strategy.

He says, "I will think of the number before 40." I wonder whose way will be, whose strategy will be quicker.

Which way did you prefer and why? So you may have decided that you could count on from 30 and you might have felt more confident counting forwards.

I think I perhaps might have chosen Lucas' strategy because I think it would be quicker to say 40, and then just go back to 39.

So there's Aisha and she says, "I start my count from 30 and I count, "31, 32, 33, 34, 35, 36, 37, 38, 39 40." Lucas says, "The number before a decade number "always ends in nine.

"I know the number is in the 30s, it must be 39." Mm.

So two strategies there.

They both got you the right answer.

I wonder which one you preferred.

Did you spot another number that could have helped you there? Yes, you might have spotted the 35.

Aisha says," I could have started my count "from 35 instead of 30." So if you don't feel confident counting backwards, but you feel more confident counting forwards, you don't have to start at 30.

You can start at 35, can't you? I start my count from 35 and I count 36, 37, 38, 39, 40.

Lucas and Aisha are playing, I'm Thinking of a Number.

They each pick a number from the number track and describe it.

Aisha says, "I'm thinking of a number.

"It is in the 20s.

"It ends in five.

"What is my number?" And Lucas guesses 25 because that's in the 20s and it ends in the five.

It's the only one it could be, isn't it? Then Lucas takes a turn.

"I'm thinking of a number.

"It is between 30 and 40.

"It is after 38.

"What is my number?" And Aisha guesses 39 because it's in the 30s and 39 comes after 38, doesn't it? Well done.

So your task for the next part of today's lesson now is to pick a number from your 100 square or the number track.

Work in pairs to play I'm Thinking of a Number.

So Aisha's showing us here.

She says, "I will give you some clues about my number." And then Lucas, her partner says, "I will guess your number.

"And when I find your number, "I will pick a number to describe." Okay, so work with a partner and describe a number.

And when they've guessed it, then they can have a turn to describe and give clues, can't they? And here's some words to help you.

You might think of using the word before or after or between.

So pause the video now while you try that activity.

Okay, so let's see how we got on.

Here's Aisha and Lucas.

And Aisha's saying, "I'm thinking of a number.

"It is in the 20s.

"It is before 22.

"What is my number?" And then Lucas guesses 21 because that's the number before 22, isn't it? And then Lucas comes up with an example.

"I'm thinking of a number.

"It ends in five.

"It is between 30 and 40.

"What is my number?" So we know that it must be in the 30s, and if it ends in five then it must be 35.

That's right.

So well done, you've worked really hard using the patterns in numbers and different strategies to find missing numbers.

So that's excellent work, isn't it? Well done.

So let's think about what we've learned in today's lesson.

So we found out you can find missing numbers on number tracks in different ways.

You can use different strategies, can't you? You can count forwards or backwards to find a number.

You can look at the number before or after the missing number to help find it.

You can find missing numbers on a number track by looking at the numbers it comes in between.

And you can use the patterns in numbers to work out new facts and find out about larger numbers, can't you? So well done, you've worked really hard using what you already know to help you with new learning.

That's excellent.

Well done.