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Hello, I'm Mrs Cayley, and I'm going to help you with today's lesson.
So in today's lesson, we're going to use our knowledge of known facts and unitizing to help us to add and subtract multiples of ten.
So let's have a look at today's lesson outcome.
Here's the outcome of today's lesson.
I can use knowledge of known facts and unitizing to add and subtract multiples of ten.
Here are the keywords for today's lesson.
Can you repeat them after me? My turn, add, your turn.
My turn, plus, your turn.
My turn, subtract, your turn.
My turn, minus, your turn.
Well done, you might have used these words before.
Look out for them in today's lesson.
Here's today's lesson outline.
We're going to use knowledge of facts and unitizing to add and subtract multiples of ten.
We'll start with adding multiples of 10 and then we'll move on to subtracting multiples of 10.
So let's start with the lesson.
Here are some children that are going to help us today.
We've got Alex and Aisha.
Alex and Aisha have some cubes.
How many cubes do they have? Can you see, they've got some blue cubes and some red cubes? Alex said, "There are 3 blue cubes." Aisha said, "There are 2 red cubes." How many is that altogether? Alex said, "2 more than 3 is 5." "3 plus 2 is equal to 5." "The 3 represents 3 blue cubes," and "The 2 represents 2 red cubes." "The 5 represents the total number of cubes." Here's a stem sentence to help us.
Can you say it with me? The 3 represents the 3 blue cubes and 2 represents 2 red cubes.
The 5 represents the total number of cubes.
Alex and Aisha have represented their cubes on part-part-whole models.
Alex said, "I have drawn a bar model." Can you see his bar model there? He's got 5 as the whole and 3 and 2 as the parts.
Aisha said, "I have drawn a part-part-whole model." Can you see her part-part-whole model there? It also shows 5 as the whole and 3 and 2 as the parts.
Alex said, "The 3 represents 3 blue cubes." Aisha said, "The 2 represents 2 red cubes." So that's the same for both of their part-part-whole models.
Alex said, "The 5 represents the total number of cubes." Here's a stem sentence to help us.
Can you say it with me? The 3 represents the 3 blue cubes and 2 represents 2 red cubes.
The 5 represents the total number of cubes.
So 3 ones plus 2 ones is equal to 5 ones.
Alex and Aisha have some groups of ten cubes.
How many cubes do they have? Can you see the groups of 10 cubes? We've got three groups of 10 blue cubes, and two groups of 10 red cubes.
I wonder how many that is altogether.
Alex said" "There are 30 blue cubes." Aisha said, "There are 20 red cubes." "20 more than 30 is 50." "So 3 tens plus 2 tens is equal to 5 tens, so 30 plus 20 is equal to 50." "The 30 represents 3 tens." "The 20 represents 2 tens." "The 50 represents the total number of cubes." Let's say the stem sentence together.
The 30 represents the 3 tens and 20 represents 3 tens.
The 50 represents the total number of cubes.
Alex and Aisha have represented their cubes on part-part-whole models.
Alex said, "I have drawn a bar model." Can you see his bar model with 5 tens as the whole and 3 tens and 2 tens as the parts? Aisha said, "I have drawn a part-part-whole model." Can you see her part-part-whole model? She's also got 5 tens as the whole and 3 tens and 2 tens as the parts.
Alex said, "The 3 tens represents the blue cubes." Aisha said, "The 2 tens represents the red cubes." "The 5 tens represents the total number of cubes." I wonder what known fact they could have used to help them, do you remember in the earlier example, we had 3 ones plus 2 ones is equal to 5 ones? And now we've got 3 tens plus 2 tens is equal to 5 tens.
So we can use 3 ones plus 3 ones to help us work out 3 tens plus 3 tens.
Let's say the stem sentence together.
We know that 3 plus 2 is equal to 5, so 3 tens plus 2 tens is equal to 5 tens.
The straws are in bundles of 10.
How many straws in total? So Alex has got 2 tens, and we're going to add 5 tens.
That's going to make 7 tens.
I wonder what known fact could help with this one.
Alex said, "I know that 2 plus 5 is equal to 7." "So 2 tens plus 5 tens is equal to 7 tens." So how many straws are there in total? Let's say the stem sentence together.
There are 7 groups of 10, so there are 70 straws.
Alex and Aisha have represented their straws on part-part-whole models.
Alex said, "I have drawn a bar model." Can you see his bar model with 7 tens as the whole and 2 tens and 5 tens as the parts? Aisha said, "I have drawn a part-part-whole model." Can you see her part-part-whole model? It also has 7 tens as the whole, and 2 tens and 5 tens as the parts.
"The 2 tens represents 2 bundles of straws." "The 5 tens represents 5 bundles of straws." "The 7 tens represents the total number of straws." I wonder which known fact they could have used to help them work this out.
We know that 2 ones plus 5 ones is equal to 7 ones, so we can use that to help us.
Let's say the stem sentence together.
We know that 2 plus 5 is equal to 7, so 2 tens plus 5 tens is equal to 7 tens.
Let's check your understanding.
Is this true or false? Here we've got some groups of 10 cubes.
Alex said, "I know that 4 plus 2 is equal to 6." "So 4 tens plus 2 tens is equal to 6 tens." Do you think Alex and Aisha are correct? Pause the video and think about whether this is true or false.
What did you think about this one? It's true.
If we know that 4 plus 2 is equal to 6, then we know that 4 tens plus 2 tens is equal to 6 tens, and that's 60.
"So 4 tens plus 2 tens is equal to 6 tens." Here's a task for you to have a go at.
Can you match the representations to the equations? So here we've got some groups of 10, we've got some cubes and straws, and we've got the equations.
5 tens plus 2 tens is equal to 7 tens.
4 tens plus 3 tens is equal to 7 tens, and 6 tens plus 1 ten is equal to 7 tens.
Can you match the correct picture with the equations? Here's the second part of your task.
Complete the equations.
What facts do you know to help? And can you say the stem sentence each time? So here we've got 5 tens is equal to 1 ten plus, mm, tens.
5 tens is equal to two tens plus, mm, tens.
5 tens is equal to 2 tens plus, mm, tens.
5 tens is equal to 4 tens plus, mm, tens, and 5 tens is equal to 5 tens plus, mm, tens.
Think about how many more groups of 10 do we need each time and what do you notice? You could use cubes or straws to help you, and say the stem sentence.
We know that mm plus mm is equal to mm, so, mm tens, plus mm tens is equal to mm tens.
Here's the third part of your task.
Can you help Alex? Aisha said, "My answer is 8 tens.
I started with some groups of 10 and I added some groups of 10." Alex is wondering, "What equation could Aisha have completed?" You could try this out with cubes or straws, and see if you can write down an equation that she could have completed, and think about whether there's more than one possible equation that she could have completed.
So pause the video and have a go at your tasks.
How did you get on with your tasks? Did you match the representations to the equations? So the first picture had 6 tens plus 1 ten, and that's equal to 7 tens.
The middle one had 4 tens plus 3 tens, and that's also equaled 7 tens, and the bottom one had 5 tens plus 2 tens, that also makes 7 tens.
Did you notice that they all made the same total? How did you get on with the second part of your task? Did you complete the equations, and what did you notice? So here we've got 5 tens is equal to 1 ten plus 4 tens, and 5 tens is equal to 2 tens plus 3 tens.
5 tens is equal to 3 tens plus 2 tens.
5 tens is equal to 4 tens plus 1 ten, and 5 tens is equal to 5 tens plus 0 tens.
What did you notice? Aisha said, "I noticed the number of tens we knew went up by 1 each time." So the first part of the equation, the tens number is going up by 1 each time, and Alex said, "I had to add one fewer group of 10 each time." So each time we had to add one fewer group of 10.
How did you get on with the third part of your task? You might have chosen these equations.
So Aisha said, "My answer is 8 tens.
I started with some groups of 10 and I added some groups of 10," and Alex said, "Here are some I came up with.
The sum had to be 8 tens." So we could have had 8 tens is equal to 1 ten plus 7 tens, or 2 tens plus 6 tens, or 3 tens plus 5 tens.
Can you think of any other ways? We could have had 4 tens and another 4 tens, couldn't we? And we could have swapped these addends rounds as well.
So we could have had 5 tens plus 3 tens.
6 tens plus 2 tens, or 7 tens plus 1 ten.
How did you get on with that one? Let's move on to the second part of the lesson.
We will subtract multiples of ten.
Alex has 5 cubes.
Can you see his 5 cubes there? If he gives 2 to Aisha, how many cubes will he have left? Alex said, "I had 5 cubes at the start." Aisha said, "Alex gave me 2 cubes." Alex said, "2 less than 5 is 3." "So 5 subtract 2 is equal to 3." So how many cubes has Alex got left? He said, "I had 3 cubes left." I've crossed out the two cubes that he's given to Aisha, and here he's got 3 cubes left.
So 5 minus 2 is equal to 3.
What does each number in that equation represent? Let's say the stem sentence together.
The 5 represents the 5 cubes at the start, and the 2 represents the 2 cubes he gave away.
The 3 represents the cubes he had left.
Alex and Aisha have represented their cubes on part-part-whole models.
Alex said, "I have drawn a bar model." Aisha said, I have drawn a part-part-whole model." Can you see they've both got 5 as the whole and 3 and 2 as the parts? Alex said, "The 3 represents 3 cubes I had left," and Aisha said, "The 2 represents 2 cubes I had." Alex said, "The 5 represents the total number of cubes." Let's say the stem sentence together.
The 5 represents the 5 cubes at the start, and the 2 represents the 2 cubes he gave away.
The 3 represents the cubes he had left.
Alex has got some groups of 10 cubes this time.
Alex has 5 groups of 10 cubes.
If he gives 2 groups to Aisha, how many will he have left? Alex said, "I had 5 groups of 10 cubes at first." Aisha said, "Alex gave me 2 groups of 10 cubes." So I wonder how many cubes Alex is going to have left.
Alex said, "20 less than 50 is 30." "So 5 tens minus 2 tens is equal to 3 tens, So 50 minus 20 is equal to 30." So Alex will have 30 cubes left.
I've crossed out the two groups of 10 that he's given to Aisha.
Alex said, "I will have 3 tens left," and 3 tens is equal to 30, isn't it? So 5 tens minus 2 tens is equal to 3 tens, and 50 minus 20 is equal to 30.
What does each number in those equations represent? Let's say the stem sentence together.
The 50 represents the 5 tens, and 20 represents 2 tens.
The 30 represents the total number of cubes left.
So if we give 2 tens to Aisha, you can see we've got 3 tens left.
Alex and Aisha have represented their cubes on part-part-whole models.
Alex said, "I have drawn a bar model." Aisha said, "I have drawn a part-part-whole model." Can you see they've both got 5 tens as the whole and 3 tens and 2 tens as the parts? Alex said, "The 5 tens represents the cubes I had at first." Aisha said, "The 2 tens represents the cubes Alex gave me." Alex said, "The 3 tens represents the cubes I had left." So which known fact can help them work this one out? Do you remember earlier when Alex had 5 cubes and gave 2 cubes to Aisha and he had 3 cubes left? So 5 ones minus 2 ones is equal to 3 ones.
So we can use that to help us work out this one.
Let's say the stem sentence together.
We know that 5 minus 2 is equal to 3.
So 5 tens minus 2 tens is equal to 3 tens.
There we are, Alex has given 2 tens to Aisha.
Can you see he's got 3 tens left? Let's check your understanding.
Is this true or false? Alex said, "I know that 6 minus 2 is equal to 4." "So 6 tens minus 2 tens is equal to 4 tens." Do you think that's true or false? Pause the video while you think about this one.
What did you think about this one? It's true.
If we know that 6 minus 2 is equal to 4, then we know that 6 tens minus 2 tens is equal to 4 tens.
So if we cross out the 2 tens, we can see that there would be 4 tens left, and there we are, 4 tens are left.
Let's check your understanding again.
What is the missing number? Here we've got 7 tens.
7 tens minus 3 tens is equal to, mm, tens.
And think about whether you know a fact that can help you with this one.
So pause the video while you think about this one.
Do you know a fact that can help you with this one? So Alex said, "I know that 7 minus 3 is equal to 4." "So 7 tens minus 3 tens is equal to 4 tens." If we cross them out, you can see that there will be 4 tens left.
There we are, we've subtracted 3 tens, and you can see there are 4 tens left.
Here, we've got some bundles of straws.
Each bundle has got 10 straws.
The straws are in bundles of 10, and Alex has 8 bundles of 10.
He gives 5 bundles to Aisha.
How many will he have left? I wonder if you know a fact that can help with this one.
Alex said, "I know that 8 minus 5 is equal to 3." "So 8 tens minus 5 tens is equal to 3 tens." So 8 tens subtract 5 tens is equal to 3 tens.
So if we cross out five of the tens, can you see that there'll be 3 tens left? How many straws are left? I can see there are 3 groups of 10 left.
Let's say the stem sentence together.
There are 3 groups of 10, so there are 30 straws left.
So if we subtract 5 tens, you can see that there are 3 tens left and that's 30.
Alex and Aisha have represented their straws on part-part-whole models.
Alex said, "I have drawn a bar model." Aisha said, "I have drawn a part-part-whole model." Can you see that they've both got 8 tens as the whole, and 5 tens and 3 tens as the parts? I wonder what each number represents.
Alex said, "The 8 tens represents the total bundles of straws." Aisha said, "The 5 tens represents 5 bundles of straws." They're the ones that he gave away.
Alex said, "The 3 tens represents the number of straws left." And which known fact helped us with this one? It was 8 minus 5 is equal to 3.
So let's say the stem sentence together.
We know that 8 minus 5 is equal to 3, so 8 tens minus 5 tens is equal to 3 tens.
Here's a task for you to have a go at.
Here we've got some groups of 10 cubes or straws.
Can you see some of them have been crossed out? So they're going to be subtracted from the total.
Can you match the representations to the equations? I can see that all of our equations are starting with 6 tens, but we're subtracting a different number of tens each time.
See if you can match the correct equation to their representations.
Here's the second part of your task.
Can you complete the equations? Each time we're starting with 5 tens and we're subtracting a different amount of tens.
Think about how many groups of 10 will be left, and what do you notice? You could use cubes or bundles of straws to help you.
So pause the video and have a go at your tasks.
How did you get on with your tasks? Did you match the representations to the equations? So in the first example, we had 6 tens, and we have subtracted 2 tens, and that will leave us with 4 tens.
Then we've got 6 bundles of 10 straws, and we're going to subtract 3 tens and that will leave us with 3 tens.
And finally, we've got 6 groups of 10, and we're going to subtract 1 ten, and that will leave us with 5 tens.
How did you get on with the second part of your task? Did you complete the equations? And did you work out how many groups of 10 were left? So here we've got 5 tens minus 1 ten is equal to 4 tens.
5 tens minus 2 tens is equal to 3 tens.
5 tens minus 3 tens is equal to 2 tens.
5 tens minus 4 tens is equal to 1 ten, and 5 tens minus 5 tens is equal to 0 tens.
What did you notice? Did you spot that the difference decreased by one group of 10 each time? So each time we started with 5 tens, and we subtracted one more group of 10 each time, and we were left with one fewer group of 10 each time.
So the difference decreases by 10 each time.
We've got to the end of our lesson.
Today, we were using knowledge of facts and unitizing to add and subtract multiples of 10, and this is what we've learned.
Tens numbers can be added to or subtracted from a multiple of 10.
When you add 10 to a number, the tens number increases by one.
And when you subtract 10 from a multiple of 10, the tens number decreases by one.
Known facts can help you to add and subtract multiples of 10.
For example, if 3 plus 2 is equal to 5, then 3 tens plus 2 tens is equal to 5 tens.
And if 5 minus 2 is equal to 3, then 5 tens minus 2 tens is equal to 3 tens.
So you can always try to use known facts to help you work out equations like this.
Well done, everyone, see you soon!.
