Lesson video

Hello everyone, my name is Mrs. Kelly and I will be taking your lesson for today.

In the previous lesson, you were set the following activity.

You have to sort some expressions into three groups.

So each expression would match one of those groups.

The first group are expressions that had a sum less than 10.

The second group were expressions with a sum equal to 10.

And the third group were expressions which equal to sum, more than 10.

So let's look at the first expression.

Eight add two.

Now, if I'm remembering correctly, 10 is made of eight and two, two and eight.

Which means, that eight and two should fit in my second group because eight and two is equal to 10.

Seven add one.

Well, I know that 10 is made of seven and three, three and seven, but hang on.

I haven't got three here, I've got one.

And one is less than three, which means that this expression will be equal to a sum less than 10.

And finally, six add six.

Six is made, 10 is made of six and four, four and six.

But I haven't got the addend four here, I've got the addend six.

And seeing a six is more than four, this means this expression will be more than 10.

It will be equal to more than 10.

Here is an equation.

10 subtract six is equal to a missing number.

Now I can calculate this.

I can start at 10 on my number line because that's my whole.

And I can come back, I can come back six.

So let's see how we do that.

One, two, three, four, five, six.

10 subtract six is equal to four.

Now I want you to hold up your hands for me.

We're going to do that on our fingers too.

So what we're going to do, we're going to hold up 10 fingers and we're going to subtract six of them.

So watch me very very carefully.

10 subtract six.

And what number am I left with? Let's see on the screen too.

That's right.

I'm left with four fingers.

But I don't know about you.

I think this takes a very very long time.

Is there a better way to subtract six rather than counting back in ones? So let's think about what we already know about these numbers.

So I can represent these, these numbers in, in the equation as a bar model.

So I know that 10 is my whole.

So I'm going to put that in the whole bar on my bar model.

And six is a part.

So I'm going to put that beneath my whole.

And I know my missing number is the other part.

And I already know that my missing number is four.

So I can put that also beneath my, my whole and next to my other part six.

I wonder, what do you notice about these numbers? Pause the video if you want to think or to discuss with somebody in your house.

Now, I know what I notice.

10 is made of six and four, four and six.

That's much better because if I know my addition past 10, this can also help me with my subtraction.

So our bar model is very very clever.

Because we can cover up six, which leaves us with four.

So we can say 10 subtract six is equal to four.

But what we can also say, is if we cover up the four, 10 subtract four is equal to six.

So this would explain why counting back in once on the number line isn't needed.

We don't need to count back to subtract from 10.

Because we can use our knowledge of pairs of numbers that sum to 10.

In this case, 10 is made of six and four, four and six.

It's not just about getting to the answer.

It's about making connections and using what you know.

So let's look at another equation.

A missing number is equal to 10 subtract two.

Now I know that 10 is my whole.

So I'm going to put that in the whole bar or my bar model.

And two is one of my parts.

So that can go beneath the whole.

Now, I don't know what my missing number is, but what I can do is think about number pairs that sum to 10, which have two as one of their numbers.

So have a pause.

What number pairs that sum to 10, have a two as one of their numbers? Pause the video, or have a discussion with somebody.

So let's go through our number bonds.

10 is made of 10 and zero, zero and 10.

Haven't said a number two yet.

So let's go to the next one.

10 is made of nine and one, one and nine.

Nope.

I've not had the number two yet.

10 is made of eight and two, two and eight.

That's it.

10 is made of eight and two, two and eight.

My missing number is eight.

We don't need to subtract in ones.

We can use our knowledge of pairs and number pairs that sum to 10.

10 is made of eight and two, two and eight.

Which means 10 subtract two must be eight.

So we've got another equation here.

10 subtract a missing number is equal to nine.

Now let's have a think.

10 is our whole, so that's going to go in the whole bar on our bar model.

And nine is one of our parts.

So that can go in the bar beneath my whole.

Now I don't know what my missing number is, but I am going to have a think.

What number pairs that sum to 10, have a nine as one of their numbers.

Pause the video to have a discussion with someone or to have a think.

Now we're going to go through our number bonds again and see if we can see here, the number nine pop up in them.

So, 10 is made of 10 and zero, zero and 10.

I can't hear the number nine, let's go to the next one.

10 is made of nine and one, one and nine.

Did you just hear the number nine? I did.

10 is made of nine and one, one and nine.

This means my missing number must be one.

10 subtract one is equal to nine.

Now, we have a lot of equations here.

Let me read them for you.

10 subtract four is equal to something or missing number.

10 subtract five is equal to a missing number.

10 subtract six is equal to a missing number.

And 10 subtract seven is equal to a missing number.

Can you see any connections? Pause the video if you want to think, or to discuss with someone.

Remember, we can use our knowledge of number pairs to 10, to subtract from 10.

So let's remember our chance.

Let's go for it before we do these questions.

10 is made of 10 and zero, zero and 10.

10 is made of nine and one, one and nine.

10 is made of eight and two, two and eight.

10 is made of seven and three, three and seven.

10 is made of six and four, four and six.

10 is made of five and five.

So, let's look at the first one.

10 subtract four is equal to something.

So I can draw my bar model with 10 as my whole and four as one of my parts.

And let's remember our chance.

10 is made of six and four, four and six.

Six is our missing number, because four and six add together to, add together to equal 10.

Let's go to the next one.

10 subtract five.

10 is made of five and five.

Which means my missing number must be five.

10 subtract six.

10 is made of six and four, four and six.

My missing number is four.

10 subtract six is equal to four.

What about 10 subtract seven? 10 is made of seven and three, three and seven.

So three must be our missing number.

So let's look at these equations now.

Can you spot a pattern? Pause the video if you want to think, or to discuss with someone.

So remember we can use our knowledge of number pairs to 10, to subtract from 10.

So let's have a think about the first one.

10 subtract a missing number is equal to 10.

Now it looks like that number 10 appears at the beginning of my equation and also at the end.

Which means that we haven't subtracted anything.

So we've got nothing to show on our bar model.

So we've got 10 here, We've got zero here, and 10 below my whole.

10 is made of 10 and zero, zero and 10 10 subtract a missing number is equal to two.

So, let's think about pairs of numbers.

10 is made of eight and two, two and eight.

Which means my missing number must be eight.

And two goes down my bar model.

So 10 subtract eight is equal to two.

Next one.

10 subtract a missing number is equal to four.

Now 10 is made of six and four, four and six.

So that means my missing number, my missing part is six.

And again, I've got the zero coming up but I'm one step ahead now.

10 is made of 10 and zero, zero and 10.

Remember, because we've got zero as one of our parts, we've got nothing to show in the bar model.

So that won't be there.

But we can show our whole, which is 10.

And our missing part which is 10.

So here's your practise activity for today.

I would like you to fill in the missing numbers for each equation and draw a bar model to show the relationship between the numbers for each equation.

For example, if I've got 10 subtract one.

10 is my whole and I'm going to put that at the top of my bar model.

And one is my part, so that can go underneath.

And all I've got to work out is what my missing number's going to be.

And I can use my number bond pairs to work that out.

10 is made of nine and one, one and nine.

I wonder what the missing part, the missing number is going to be.