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 Crossing the Tens boundary Counting Backwards, and it comes from the unit patterns and counting from 20 to 100.

So you're going to be looking for those patterns when you are crossing the tens boundary, counting backwards and seeing how they can help you.

Okay, and by the end of today's lesson, you should feel much more confident with counting backwards across that boundary.

So our words are going to be important for our learning today.

Our keywords are cross the tens boundary.

So my turn, cross the tens boundary, your turn.

And tens boundary, my turn, tens boundary, your turn.

And decade number, my turn, decade number, your turn.

Excellent, well done.

So in the first part of today's lesson, we're going to look at crossing the tens boundary when we're counting backwards from 50 and then we'll move in the second part of today's lesson onto counting backwards from 100.

In this lesson you will meet Aisha and you'll also meet Lucas.

They'll be helping us with our learning today.

So here we've got a 100 square and we're going to start at 50 and count backwards along the 100 square.

When you reach 41, what will the next number in your count be? Let's try and see.

So 50, 49, 48, 47, 46, 45, 44, 43, 42, 41.

Where will we go now? That's right, we go to 40, don't we? We go to the end of the row before.

So we're going to continue to count backwards along the 100 square pointing to each number as we count.

All right, so we're on 40, 39, 38, 37, 36, 35, 34, 33, 32, 31, 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, nine, eight, seven, six, five, four, three, two, one.

Excellent, well done, brilliant counting.

Aisha and Lucas have been using the patterns in numbers to help them count backwards from 100.

And there's Aisha and she's saying, "Can you count backwards from 34?" And Lucas says, "I'm finding some parts quite tricky." Count backwards from 34 to help Lucas and use your 100 square to help you.

So let's do that together.

34, 33, 32, 31, 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, nine, eight, seven, six, five, four, three, two, one.

Excellent work, which was the hardest part? That's right when you cross that tens boundary, that's the tricky bit, isn't it? When you reach a new decade number, it is called the tens boundary.

Crossing the tens boundary can be difficult to remember because the pattern changes.

What do you notice about the decade numbers and the numbers that come before them? So we've got 40 and then we've got the thirties, we've got 30, and then we've got the twenties.

Did you notice they begin in a different way, don't they? So you can see 30, but then it goes into the twenties and they all have a 20 at the start.

The row before the decade number starts differently, doesn't it? So before 50 is the forties, before 40, it is the thirties, before 30 is the twenties and so on.

Lucas and Aisha are trying to put the 100 square back together.

Lucas finds a decade numbers shown, he's got 40 and Aisha is looking for the numbers that go before it.

Which ones should she look for? That's right.

She should look for the thirties, shouldn't she? Because before the forties comes the thirties, there they are.

Aisha is counting backwards from 40.

40, 49, 48, 47.

What mistake has been made, what did she do? She needed to count the row before 40, which is the thirties.

So when you count 40 and you go backwards, it goes to the thirties and there they are.

So, now time to check your understanding.

So, when counting backwards, which number comes before four? Is it 49, is it 39 or is it 29? Pause the video now while you have a try at that.

And how did we do, let's have a look.

So did you spot that when you count backwards from 40, you need to go into the 30.

So it must be 39, well done.

We can see the tens boundary on the 100 square, can't we? There it is, it's a decade numbers.

That's where the pattern of counting changes.

Lucas says, I've noticed something about all the numbers before the decade numbers.

I wonder what he's noticed.

The numbers before the decade numbers all end in nine.

Count backwards from each decade number and we can use what we've just found out to help us, can't we? 40, 39, that's right.

And then 38 and then we can go 30, 29, 28.

And then we could say 50, 49, 48, that's right.

Count backwards from the decade number.

So we can see we've got 40 here, haven't we? So 39, 38, 37, 36, 35, 34, 33, 32, 31.

Now time to check your understanding again.

So here's Lucas and he says, "I'm thinking of a number from the row below.

What number could I be thinking of?" So we can see he's got a row from the 100 square which has 50 at the end.

So pause a video while you think of what other numbers could be on that row.

Okay, what did we come up with? Let's see what answers you could have had, so there's 50.

So you could have had 49, 48, 47, 46, 45, 44, 43, 42 or 41.

Could you have had any other numbers? You couldn't, could you? Because they're the only numbers that are on that row on the 100 square.

You can practise crossing the tens boundary when counting backwards on a 100 square.

So there we can count backwards from 43, can't we? So 43, 42, 41.

Where will you look to continue your count when you reach the start of that row? That's right, so you'll go to 40, won't you, and then 39, 38 and so on.

So now we can count backwards from 32.

Think about what the decade before the thirties will be to help you.

So 32, 31, where will you go? That's right, you'll go to 30 then 29, 28, that's right.

So count backwards and cross the tens boundary on the number track.

So instead of doing it on a 100 square this time, we're trying on an odd number track.

So 34, 33, 32, 31, 30, 29, 28, 27, 26, 25.

Well done, did you spot that when you go from the thirties, you go into the twenties when counting backwards.

Where was the tens boundary? Can you spot it, that's right where the pattern of counting changes when you go from 30 to 20, so it's 30, 29.

So now it's time to check your understanding again.

So count backwards across the tens boundary and you're starting at 45.

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

Okay, and now let's do it together.

45, 44, 43, 42, 41, 40, 39, 38, 37, 36.

Where was the tens boundary, did you spot it? That's right, it's where the pattern changed.

So it went from 40 to 39, that's right.

So for the first part of your lesson, the task is here, it says cut out the numbers shown and put them in the correct places on the missing number strips.

Okay, so you're cutting out the numbers there, 28, 29 and so on, and then you'll put them in the right order on those number strips.

So pause the video now while you try that activity.

Okay, and now let's see how we got on with that.

First strip has a 50 in the middle, so we know we'll have 52, 51 and then 50 49, 48, won't we? That's right, so you know you'll have some numbers in the early fifties there and you'll have some numbers in the forties as well, that's right.

Okay, and then which numbers, we'll go where with the 40 strips.

So we've got 42, 41, 40, 39, 38.

So I counted backwards to help me, didn't I? And then 30, so we've got 32, 31, 29 and 28 there, haven't we? Excellent, well done.

You've worked really hard in the first part of our lesson.

So now we're going to move on to crossing the tens boundary counting backwards, but this time with numbers up to 100.

So count backwards from each decade number.

So we've got 70 and then we're going to go 69, 68, 67, 66, 65, 64, 63, 62, 61.

Okay, and then we'll count backwards from 100.

So 100, 99, 98, 97, 96, 95, 94, 93, 92, 91.

Well done, that was fantastic counting.

So now it's time to check your understanding again, you are going to count backwards from the decade number 80.

So pause the video while you try that.

And now we're going to do it together.

80, 79, 78, 77, 76, 75, 74, 73, 72, 71.

Well done, that was fantastic.

Which row comes before the nineties? What do you think it is? That's right, it's the eighties.

What comes before the eighties? That's right, the seventies and then it will be the sixties and what comes before the sixties, the fifties.

That's right.

Now it's time to check your understanding again.

So here's Aisha and she says, "Look at this row, I think this is the sixties." What mistake has been made.

So pause a video while you think about that.

What was the mistake there then? So you can see 60 is at the end of the fifties.

You must look at the numbers at the start of the row to find out.

So that row is the fifties row, isn't it? And another check here, okay, so Aisha has put on all the rows she has found so far, she's now looking for this one, the one with the green box around it.

Which row should she be looking for? Okay, so pause the video, okay? Think about what we've done so far to help you and then have a try at that.

So let's have a look, how did you get on? So we can see we've got the nineties row at the bottom, then the eighties, then the seventies, then the sixties.

So she must be looking for the fifties, that's right.

The number track shows the numbers before the decade numbers.

What's the same about them all and what's different? So we can see the decade numbers there.

So you look at the numbers before the decade numbers.

So there they are, 59, 69, 79.

So what's the same about them all and what's different? So what's the same is that they all end in a nine, don't they? But what's different is they all start in a different way to the decade number.

So we go from 60 to 59, 70, 69, and from 80 to 79.

The pattern changes because you have crossed the tens boundary.

The number track shows the decades.

We can see the seventies, we can see the sixties and we can see the fifties.

Point to the tens boundaries, can you see them? That's right, we've got where the seventies goes to the sixties and where the sixties goes to the fifties.

What do you notice about the numbers that come before the decade numbers? They all end in a nine, don't they? Yes, well spotted.

So, time to check your understanding again now.

Match each decade number to the number that comes before it.

So we've got 90, 70, 80, and then on the other side, 69, 79, 89.

Pause the video while you try that.

Okay, so the number before 90 will be, that's right, 89 and the number before 70 will be 69.

And the number before 80 will be 79, excellent.

So Lucas is here and he says, "I'm thinking of a number from the row below.

What number could I be thinking of?" Aisha here says, "You could be thinking of 89." Explain why can't Aisha be right? That's right, because 80 comes at the end of the seventies row, so Lucas's number must begin with 70, it must be 70 something.

The seventies row comes before 80, doesn't it? So it could be 79 or 78, 77, 76, 75, 74, 73, 72, 71.

But it definitely couldn't be 89 because that would be in the eighties row, not the seventies row.

You can practise crossing the tens boundary when counting backwards on a 100 square.

So let's try that.

We've got 93, 92, 91.

Where will you look to continue your count? When you reach the start of the row.

So while we go from 91, that's right, we go to 90 at the end of the row before, don't we? And then we could count 89, 88, let's do the same and practise counting backwards from 82, 82, 81.

Where will we go? That's right, we'll go to 80, 79, 78.

So time to check your understanding again, count backwards from the number shown until you have crossed the tens boundary.

So we're starting at 72, okay, and you're counting backwards.

So pause the video, okay? You don't have to go all the way back to the start of the 100 square, but make sure you stop counting after you've crossed tens boundary.

Okay, so let's try that together.

72, 71, 70, 69, 68 and you may have counted a little bit further back than that.

Count backwards along the number track and cross the tens boundary.

So we're starting at 64 and we're going to count backwards.

64, 63, 62, 61, 60, 59, 58, 57, 56, 55.

Where was the tens boundary? Did you spot it? That's right, it was where the pattern of counting changed, didn't it? So it went from 60 to 59.

So time to check your understanding again.

So you're going to count back along this number track and you are starting your count at 84.

So pause the video while you do that.

Okay, and let's do it together.

84, 83, 82, 81, 80, 79, 78, 77, 76, 75, well done.

Where was the tens boundary, did you spot it? That's right, where it went from the eighties to the seventies, 80, 79.

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

Lucas says, "I will pick a number card and I will count back from that number." And Aisha says, "We will take it in turns to say the numbers in the same count." So Lucas might say 65, he might pick the number 65 and then Aisha would say 64, 63, 62, 61, 60, 59, 58 and so on.

Stop counting when you cross the tens boundary twice.

So they only crossed it once, didn't they? It went from the sixties to the fifties, but you have to cross it twice in this activity.

So pause the video now while you try that.

So let's see how we got on.

So we've got Lucas and Aisha showing us how they did it, okay.

So we've got, Lucas says, "I picked 65, so I said that number." And then Aisha says, "I said the number before 65." So we've got 65, 64, 63, 62, 61, 60, 59.

So we've crossed that tens boundary once, haven't we? 58, and then they have to cross it twice.

So they would keep counting, they would go 57, 56, 55, 54, 53, 52, 51, 50, 49.

And then they can stop counting because they've crossed the tens boundary twice.

So, excellent, well done, that was fantastic counting today.

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

So we found out that the numbers from zero to 100 have patterns that can help us to count backwards when we cross the tens boundary.

They are arranged differently on our number track and on a 100 square.

We can count them in two ways, the numbers can't we? So we can say three tens, nine, or we can say 39.

And a number ending in a nine always comes before a decade number when we're counting in ones.

So that's excellent work.

You've worked really hard using those patterns to help you when you've been crossing the tens boundary.

I've really enjoyed our work today, well done.