Lesson video

Hello, I'm Mrs. Kaylee and I'm really pleased to be learning with you today.

So in today's lesson we'll be using addition and subtraction facts within 10 to help us to add and subtract within 20.

So if you already know some addition and subtraction facts within 10, like 5 plus 5 is equal to 10 or 5 plus 3 is equal to 8 or 8 minus 4 is equal to 4, then we can use these to help us to add and subtract up to 20.

So let's have a look at today's lesson outcome.

Here's the outcome of today's lesson.

I can use knowledge of addition and subtraction facts within 10 to add and subtract within 20.

Here are the keywords for today's lesson.

Can you say them after me? My turn, addition.

Your turn.

My turn, subtraction.

Your turn.

My turn, plus.

Your turn.

My turn, minus.

Your turn.

So you might have seen these words before.

Look out for them in today's lesson.

Here's today's lesson outline.

We'll start off by using inequalities and then we'll move on to addition and subtraction problems. Let's start on the learning.

Here are some children that are going to help us today.

We've got Jacob and Laura.

Laura and Jacob are comparing their pencils and pens.

I wonder how many pencils they've got? Can you see a group of 10 and some ones? They've got 15 pencils, haven't they? Then they've got some pens.

They've also got a group of 10 and some ones.

So how many pens have they got? There are 17 pens, aren't there? Laura said, "We have 15 pencils." Jacob said, "We have 17 pens." They're going to compare the amount of pencils and pens.

So we're going to see which one has got more and which one has got fewer.

Laura said, "15 is less than 17." Can you see there are fewer pencils and there are pens? Jacob said, "17 is greater than 15." Can you see there are more pens and there are pencils.

Laura has noticed that 15 is 10 plus 5.

Jacob has noticed that 17 is 10 plus 7.

Can you see anything that's the same about both of those? So because they've both got one 10, we only need to look at the ones don't we? So Laura said, "10 plus 5 is less than 10 plus 7." And Jacob said, "10 plus 7 is greater than 10 plus 5." We can compare the amounts on a number line.

So for the pencils, we had 10 plus 5, and that's equal to 15.

And for the pens we had 10 plus 7, that's equal to 17.

Can you see which one is greater? So 10 plus 7 is greater than 10 plus 5.

Why is 10 plus 7 greater than 10 plus 5? Let's try saying the stem sentence.

10 plus 7 is greater than 10 plus 5 because 7 is greater than 5.

7 ones is greater than 5 ones.

So if 10 plus 7 is greater than 10 plus 5, then 10 plus 5 must be less than 10 plus 7.

So here we've got another stem sentence, 10 plus 5 is less than 10 plus 7 because, now we know that they've both got one 10, so we just need to compare the ones.

So 5 is less than 7, 5 ones is less than 7 ones.

Let's check your understanding.

Are these true or false? So the first one says 15 is greater than 10.

The next one says 15 is less than 13.

Then we've got 17 is greater than 10 plus 5.

And finally we've got 15 is less than 10 plus 3.

You could look on a number line to help you check these, so pause the video and have a think about these ones.

What did you think about these ones? So the first one says 15 is greater than 10.

That's true, isn't it? The second one says 15 is less than 13.

No, that's not right.

15 is greater than 13, isn't it? Than because 15 is 10 plus 5 and 13 is only 10 plus 3.

What about the next one? 17 is greater than 10 plus 5.

That one is correct.

Laura said, "I know that 7 is greater than 5 "so 17 is greater than 10 plus 5." 17 is made of 10 plus 7, isn't it? So 10 plus 7 is greater than 10 plus 5.

That's like our pens and pencils that we looked at earlier.

What about the last one? 15 is less than 10 plus 3.

That's not right, is it? Jacob said, "I know 5 is greater than 3 "so 15 is greater than 10 plus 3." 15 is made of 10 plus 5, so that's going to be greater than 10 plus 3, isn't it? We can use symbols to compare numbers and equations, they're called the equality and inequality symbols.

So we can use equal to, greater than, or less than symbols to compare the numbers and the equations.

Laura and Jacob are wondering which is greater, 12 plus 1 or 12 plus 2.

So here we've got 12 plus 1 and then we've got a circle for the missing symbol, and is it greater than or less than 12 plus 2? Laura has noticed that they both have 12.

Jacob has noticed that we are adding 1 or 2 onto 12.

Laura said, "I know that 1 is less than 2." Jacob said, "So we are adding more "onto the second equation." So do you think 12 plus 1 will be greater than or less than 12 plus 2? Laura said, "So 12 plus 1 is less than 12 plus 2." So we're going to put the less than symbol in between those two equations.

Jacob said, "We can check.

"13 is less than 14." So 12 plus 1 is 13 and 12 plus 2 is 14.

And 13 is less than 14, so that's how we can check.

12 plus 1 is less than 12 plus 2 because 1 is less than 2.

So they both had 12 in them, so we were just looking at the extra part, weren't we? So 1 is less than 2.

We can show this on a number line.

Can you see we've got 12 plus 1, that's equal to 13.

And we've got 12 plus 2, that's equal to 14.

Can you see that 13 is less than 14? So 12 plus 2 is greater than 12 plus 1.

Jacob has noticed that when we add a greater part, the sum is greater, that means the total is greater.

Here's a stem sentence that can help us.

So we're going to put the numbers on the stem sentence.

Can you say it with me? 12 plus 2 is greater than 12 plus 1 because 2 is greater than 1.

The extra part that's been added on is greater on the second number line.

We can check this by looking at the total amount, the sum, 14 is greater than 13.

Let's say it together, 14 is greater than 13.

Now Laura and Jacob are wondering which is greater, 12 minus 1 or 12 minus 2.

So here we've got the two equations with a missing symbol in between.

So is it going to be 12 minus 1 is less than or greater than 12 minus 2? Laura has noticed that they both have 12, so they're both starting with 12.

Jacob has noticed that we are subtracting 1 or 2 from 12.

Laura said, "I know that 1 is less than 2." "So we are subtracting more from the second equation." So if we subtract more, will the difference be greater or less? Laura said, "So 12 minus 1 "is greater than 12 minus 2." Jacob said, "We can check.

"11 is greater than 10." So the first equation was 12 minus 1, that's equal to 11.

And the second equation was 12 minus 2, that's equal to 10.

11 is greater than 10.

Let's say the stem sentence together, 12 minus 1 is greater than 12 minus 2 because 1 is less than 2.

We can show this on a number line.

So 12 minus 1, that's shown on the top number line, is greater than 12 minus 2, because we're subtracting more on the bottom number line, aren't we? Jacob said, "When we subtract a greater part, "the difference is less." Here's a stem sentence to help us.

Let's put some numbers on the stem sentence.

Can you say it with me? 12 minus 1 is greater than 12 minus 2 because 1 is less than 2.

So that's the part that we've subtracted, isn't it? 1 is less than 2.

So 11 is greater than 10.

Let's say the stem sentence, 11 is greater than 10.

Now Laura and Jacob are wondering which is greater, 14 plus 3 or 15 plus 3.

Here we've got the two equations with the missing symbol, so 14 plus 3 and 15 plus 3.

What's the same and what's different about those two equations? So Laura said, "They are both adding 3." Jacob said, "We are starting with different numbers." Laura said, "I know that 14 is less than 15." Jacob said, "We are adding the same onto 14 and 15." So we're adding 3 both times.

So 14 plus 3 is less than 15 plus 3.

So we've put the inequality sign in there, 14 plus 3 is less than 15 plus 3.

We can check, 17 is less than 18.

So 14 plus 3 was 17, and 15 plus 3 is 18.

Let's say the stem sentence together.

14 plus 3 is less than 15 plus 3 because 14 is less than 15.

So we started with a smaller number, didn't we? And we added the same onto them both.

14 is less than 15 and we added 3 onto them both.

We can show this on a number line.

Can you see the first one is showing 14 plus 3? That's equal to 17.

And the second one is showing 15 plus 3, that's equal to 18.

So we were adding 3 to both numbers, but we started with a smaller number on the first number line and a bigger number on the second number line.

So 15 plus 3 is greater than 14 plus 3.

So Jacob said, "When we add a greater part, "the sum is greater." So can you see, we started with a greater part, didn't we, on the second number line? Let's say the STEM sentence together.

15 plus 3 is greater than 14 plus 3 because 15 is greater than 14.

So we had a different starting number, didn't we? 15 is greater than 14.

So we ended up with the sum 18 and 17, 18 is greater than 17.

Finally, Laura and Jacob are wondering which is greater, 16 minus 2 or 17 minus 2.

What's the same and what's different about those equations? So Laura has noticed that they are both subtracting 2.

"We are subtracting 2 from 16 and 17." "16 is less than 17." "We are starting with different numbers." "So 16 minus 2 is less than 17 minus 2." So there we've put the inequality symbol in.

16 minus 2 is less than 17 minus 2.

We can check, so 16 minus 2 is equal to 14 and 17 minus 2 is equal to 15.

14 is less than 15.

Let's say the stem sentence together, 16 minus 2 is less than 17 minus 2 because 16 is less than 17.

We can show this on a number line.

Can you see the first number line is showing 16 minus 2? That's equal to 14.

And the second number line is showing 17 minus 2, that's equal to 15.

17 minus 2 is greater than 16 minus 2.

Let's say the stem sentence together, 17 minus 2 is greater than 16 minus 2 because 16 is less than 17.

So the starting number, 16, was less than 17.

So the number that we ended up with, 15, is greater than 14.

Let's say the stem sentence together, 15 is greater than 14.

Let's check your understanding.

Who is correct? Here we've got 15 plus 1 and 15 plus 3.

Laura said, "I know 3 is greater than 1, "so 15 plus 1 will be greater than 15 plus 3." Jacob said, "I know 1 is less than 3, "so 15 plus 1 is less than 15 plus 3." Who do you think is correct? Pause the video while you have a think.

Who did you think was correct? It was Jacob.

1 is less than 3, so 15 plus 1 is less than 15 plus 3.

Here's a task for you to have a go at.

Can you fill in the missing numbers and symbols? So when you see a square, can you fill in the missing number? And when you see a circle, can you fill in the missing inequality symbol, equal to, less than, or greater than? So look at the numbers and the equations and compare them, seeing which one is more or less.

And think about how do you know.

When you've had a go at these ones, think about do any of these have more than one possible answer? Now remember if one of the parts is the same, then you only need to look at the other part, don't you, to compare them? You could use a number line to help you as well, so pause the video and have a go at your task.

How did you get on with your task? I filled out some numbers and symbols in the gaps.

So first of all, I put 17 is greater than 16.

Do you agree with that one? Then I've got 17 is less than 18 plus 1 because 18 plus 1 is 19, isn't it? So 17 is less than 19.

Then I've got 2 plus 10 is less than 4 plus 10.

Now I can see that they've both got a 10, so I only need to compare the other part, 2 is less than 4.

So 2 plus 10 is less than 4 plus 10.

Then we've got 17 plus 2, that's greater than 2 plus 15.

I can see that they've both got a 2, so let's just compare the other part, 17 is greater than 15.

Then we've got 17 minus 2, that's greater than 15 minus 2.

I can see that we are subtracting 2 each time, so 17 is greater than 15.

So 17 minus 2 will be greater than 15 minus 2.

Then I've got 15 plus 2 is less than 18.

15 plus 2 is 17, isn't it? So 17 is less than 18.

Then I've got 12 plus 3, that's less than 12 plus 4.

They've both got 12 in, haven't they? So we only need to compare the other part, 3 is less than 4, isn't it? So 12 plus 3 is less than 12 plus 4.

Then we've got 17 minus 4, now that's less than 17 minus 2.

I can see that we're starting with 17 each time, so if we take off a greater part, we'll end up with a smaller difference, so 17 minus 4 is less than 17 minus 2.

Then we've got 15 plus 2 is less than 16 plus 2.

I can see we're adding 2 to both of these.

I know that 15 is less than 16, so 15 plus 2 is less than 16 plus 2.

And then we had 19 minus 5, that's greater than 18 minus 5 because we started with a bigger number, didn't we? 19 is greater than 18.

So 19 minus 5 will be greater than 18 minus 5.

Did any of these have more than one possible answer? So for the first one, 17 is greater than 16, Jacob said, "Yes.

17 is greater than anything less than 17." So we could have had 16 or 15 or 14, or anything less than 17.

And 15 plus 2 is less than anything greater than 17, so we could have had 15 plus 2 is less than 18 or 19 or 20, or anything greater than 17.

So you might have had some different answers for those top two missing numbers.

Let's move on to the second part of the lesson.

We'll look at addition and subtraction problems. Laura and Jacob have 18 pencils.

Laura has 13 pencils.

How many pencils does Jacob have? Is this an addition or a subtraction problem? What would a part-part-whole model look like? So we know we've got 18 pencils in total and Laura has got 13 pencils.

So we could do 18 minus 13 to work out how many pencils Jacob has.

Laura said, "I have 13 pencils.

"Your part is hiding." Jacob said, "We could use addition to help us." So we could work out the missing part by working out 13 plus something is equal to 18.

Jacob said, "I know that 13 add 5 is equal to 18." So 5 is the missing part.

Laura said, "We could use subtraction to help us." We could do 18 minus something is equal to 13.

Laura said, "I know that 18 subtract 5 is equal to 13." So the missing part is 5.

Laura said, "You have 5 pencils." So 13 plus 5 is equal to 18.

We can use a number line to show this.

Can you see on the top number line, it's showing 13 plus 5, that's equal to 18? And the second number line is showing 18 minus 5, that's equal to 13.

So we know that 13 plus 5 is equal to 18, that's shown on the top number line.

So 18 minus 5 is equal to 13.

Let's say the stem sentence together, 13 plus 5 is equal to 18, so 18 minus 5 is equal to 13.

Laura and Jacob have 20 pens.

We can only see Laura's pens.

Laura has 13 pens.

How many pens does Jacob have? Can you see on the part-part-whole model that we know that the whole is 20, the total is 20? Laura said, "I have 13 pens.

"Your part is hiding." Jacob said, "We could use addition to help us." 13 plus something is equal to 20.

Jacob said, "I know that 13 add 7 is equal to 20." So 7 is the missing part.

Laura said, "We could use subtraction to help us." 20 minus something is equal to 13.

Laura said, "I know that 20 subtract 7 is equal to 13." "The missing part is 7." Laura said, "You have 7 pens." So 13 add 7 is equal to 20.

We can use a number line to show the pens.

We know that 13 plus 7 is equal to 20.

So 20 minus 7 is equal to 13.

Let's say the stem sentence together, 13 plus 7 is equal to 20, so 20 minus 7 is equal to 13.

Laura and Jacob are collecting the books in the classroom.

Laura has 12 books and Jacob has 5 books.

How many is this in total? Laura said, "I have 12 books." Jacob said, "I have 5 books." Do we need to add or subtract? Jacob said, "We need to add 12 and 5." What fact can we use to help? Can you think of a fact within 10 that might help us to work this one out? Jacob said, "I know 2 plus 5 is equal to 7." "So 12 plus 5 is equal to 17." "We have 17 books in total." Laura and Jacob used a known fact to help work out the equation.

Laura said, "I know that 2 plus 5 is equal to 7 "and 5 plus 2 is equal to 7." Jacob said, "So 12 plus 5 is equal to 17 "and 5 plus 12 is equal to 17." So from one known fact we can work out other facts.

Laura and Jacob have 17 books and Jacob found 2 more.

How many do they have now? Laura said, "We had 17 books." Jacob said, "I found 2 more books." Do we need to add or subtract? Jacob said, "We need to add 17 and 2." What fact can we use to help? Jacob said, "I know 7 plus 2 is equal to 9." "So 17 plus 2 is equal to 19 books." "We have 19 books now." Laura and Jacob used a known fact to help work out the equation.

They knew that 7 plus 2 is equal to 9.

So 17 plus 2 is equal to 19.

Laura said, "I know that 7 plus 2 is equal to 9 "and 2 plus 7 is equal to 9." Jacob said, "So 17 plus 2 is equal to 19 "and 2 plus 17 is equal to 19." Laura and Jacob have 19 pencils, 6 of them are writing pencils and the rest are colouring pencils.

How many are colouring pencils? Laura said, "We have 19 pencils." That's the total amount.

Jacob said, "There are 6 writing pencils." "The rest are colouring pencils." "How many are colouring pencils?" Laura said, "Do we need to add or subtract?" Jacob said, "We could subtract 6 from 19." "What fact can we use to help?" Can you think of a fact within 10 that might help with this one? Jacob said, "I know 9 minus 6 is equal to 3." "So 19 minus 6 is equal to 13 pencils." "So 6 are writing and 13 are colouring pencils." So here we've got 13 colouring pencils.

Laura and Jacob use known facts to help work out the equation.

Laura said, "I know that 9 minus 6 is equal to 3 "and 9 minus 3 is equal to 6." Jacob said, "So 19 minus 6 is equal to 13 "and 19 minus 13 is equal to 6." Laura and Jacob have 19 pencils and will hand 5 of them out.

How many will they have left? Laura said, "We have 19 pencils." That's the total.

Jacob said, "I will hand out 5 pencils." Laura said, "Do we need to add or subtract?" Jacob said, "We could subtract 5 from 19." "What fact can we use to help?" Can you think of a fact within 10 that might help with this one? Jacob said, "I know 9 minus 5 is equal to 4." "So 19 minus 5 is equal to 14." "We have 14 pencils left." Laura and Jacob used a known fact to help work out the equation.

Laura said, "I know 9 minus 5 is equal to 4 "and 9 minus 4 is equal to 5." Jacob said, "So 19 minus 5 is equal to 14 "and 19 minus 14 is equal to 5." Let's check your understanding.

Laura and Jacob are using a known fact to work out an equation.

Who is correct? Laura said, "I know that 4 plus 2 is equal to 6 "so 14 plus 2 is equal to 16." Jacob said, "I know that 4 plus 2 is equal to 6 "so 14 plus 2 is equal to 6." Pause the video and think about who is correct.

Who did you think was correct? It was Laura.

4 plus 2 is equal to 6, so 14 plus 2 is equal to 16.

Is that what you thought? Here's a task for you to have a go at.

Use the part-part-whole models to work out the problems. Which known facts can help? So the first one, A, says, "Laura and Jacob are collecting up the books.

"Laura has 13 books and Jacob has 5 books.

"How many is this in total?" Part B says, "Laura and Jacob are collecting the books "in the classroom.

"They have 12 books and Jacob found 4 more.

"How many do they have now?" Think of a known fact within 10 that will help you to work out these problems and show it on the first part-part-whole model and then see if you can solve the problem on the second part-part-whole model and write the equations at the bottom.

Here's two more for you to have a go at.

"Laura and Jacob have 14 books.

"3 books are red and the rest are green.

"How many are green?" And finally, "Laura and Jacob have 14 books.

"They hand out 4 of them.

How many are left?" Here's the second part of your task.

Can you use a known fact to work out the problems? Part A says, "Laura and Jacob are collecting up the books.

"Laura has 15 books and Jacob has 4 books.

"How many is this in total?" And what known fact can you use? Part B says, "Laura and Jacob are collecting up the books "in the classroom.

"They have 12 books and Jacob found 3 more.

"How many do they have now?" And what known fact can you use to help you? Part C says, "Laura and Jacob have 14 pens.

"2 pens are red and the rest are green.

"How many are green?" And what known fact can you use? Finally, "Laura and Jacob have 16 pencils.

"They hand out some and they have 4 left.

"How many did they hand out?" And what's the known fact that you could use to help you? You could use part-part-whole models or number lines to help you.

So pause the video while you have a got your tasks.

How did you get on with your tasks? Did you work out the problems and which known facts can help? So first of all, "Laura and Jacob are collecting up the books.

"Laura has 13 books and Jacob has 5 books.

"How many is this in total?" Well, you could use the known fact, 3 plus 5 is equal to 8 to help you with this one.

So 13 plus 5 is equal to 18, so there are 18 books in total.

Then in part B, "Laura and Jacob are collecting up the books "in the classroom.

"They have 12 books and Jacob found 4 more.

"How many do they have now?" So you could use the known fact, 2 plus 4 is equal to 6 to help you with this one.

12 plus 4 is equal to 16, so there are 16 books now.

Part C said, "Laura and Jacob have 14 books.

"3 books are red and the rest are green.

"How many are green?" So you can use the known fact, 4 minus 3 is equal to 1.

So 14 minus 3 is equal to 11, so 11 of the books are green.

Finally, "Laura and Jacob have 14 books.

"They hand out 4 of them.

How many are left?" So I can see the known fact, 4 minus 4 is equal to zero can help you to work out 14 minus 4, and that's equal to 10, so there are 10 books left.

How did you get on with the second part of the task? Did you use a known fact to work out the problems? So first of all, "Laura and Jacob are collecting up the books.

"Laura has 15 books and Jacob has 4 books.

"How many is this in total?" It's 19, and you can use 5 plus 4 is equal to 9 to help.

Part B, "Laura and Jacob are collecting up the books "in the classroom.

"They have 12 books and Jacob found 3 more.

"How many do they have now?" It's 15 books.

The known fact is 2 plus 3 is equal to 5.

Part C, "Laura and Jacob have 14 pens.

"2 pens are red and the rest are green.

"How many are green?" It's 12, and the known fact is 4 minus 2 is equal to 2.

Finally, "Laura and Jacob have 16 pencils.

"They hand out some and have 4 left.

"How many did they hand out?" The answer is 12.

The known fact is 6 minus 4 is equal to 2.

How did you get on with those ones? We've come to the end of our lesson.

Today we were using our knowledge of addition and subtraction facts within 10 to add and subtract within 20.

We found out that addition facts within 10 can be applied to addition within 20.

For example, if 3 plus 2 is equal to 5, then 13 plus 2 is equal to 15.

Subtraction facts within 10 can be applied to subtraction within 20.

For example, if 5 minus 2 is equal to 3, then 15 minus 2 is equal to 13.

Well done everyone, see you soon.