Lesson video

I'm Mrs. Crane and welcome to today's lesson.

We're going to be carrying on our unit, which is exploring the calculation strategies and today going be subtracting two two digit numbers using the column method.

For this lesson, you will need a pencil and some paper.

Please pause the video now to go and get these things if you haven't got them already.

Welcome back.

I thought I'd do a quick update on how Arlo is getting on.

So we went for a walk the other day down to the beach.

This is the beach in Portsmouth.

You can see here.

It's very sandy in parts but mainly pebbles and Arlo's favourite things to do is run around chase the different pebbles that he can find.

Let's get started, we're going to have a look at today's agenda.

Today we're going to be learning how to use the column method of subtracting two, two digit numbers together.

And to start with a quiz to test your knowledge, we're going to look at today's star words, we're going to be looking at petitioning and pictorial models.

Then you're going to have a chance to do your talk task, then there'll be an opportunity where we look at the column method.

We're going to look at it with dienes and the written numbers, there will be time for you to have your independent task along with the answers together and finally, there'll be a quiz to see what you have remembered.

Please pause the video now to complete your starter quiz.

Let's have a look at today's star words then, we're going to use my 10, your time, let's get started.

Place value.

Tens.

Ones.

Subtract.

Column.

Is equal to.

Lets have a look at today's new learning.

So we've got 54 we want to subtract 31 from it.

So this time I know my whole, my whole is 54 and I want to subtract 31 from it.

What don't you have a think at my question? How have I partitioned these numbers? You've got five seconds thinking time.

How have I partitioned these numbers? Well done to those of you that noticed I partitioned them into tens and ones.

For 54 there are one, two, three, four, five tens and one, two, three, four ones.

I've written it 50 plus four.

That shows me it's still 54 but it's just been partitioned.

Now this is my whole, and this is one of my parts.

All parts of that whole is made up by the number is 31.

Lets check how its been partitioned, one, two, three tens and one one.

The number is 31.

Now in order to answer and solve our equation I need to know what the other part is that makes 54.

I know one part's 31 but at the moment I don't know this part here, so let's have a go at subtracting 31 from 54 to work out what our answer is.

But as you can see here we still have the dienes that represent 54.

This time my 31 is below it because I'm going to be subtracting, checking my operation here.

I've got 54 written here as the expanders method and I've got 31 written below it.

Now I know I must start with my ones, so from my four ones I'm going to subtract one one, so imagine this one wasn't here I'd be left with one, two, three.

Well done to those of you that have counted with me.

Let's see, one, two, three, fantastic.

Now I can subtract my tens, I need to take three tens away from my five tens.

So imagining if I took away one, two, three so all these three wouldn't be here, I would be left with two, I know that they represent tens so I've got two tens and three ones.

So my number would be 20 plus three is equal to 23.

Let's look down at one more example.

Okay, our next example, says 45 subtract 32 is equal to and we don't know our number.

Again we know our whole this time, our hole is 45.

We know one of our parts is 32.

Again my question is how have I partitioned the numbers? Three seconds thinking time this time.

Well done to those of you that have said, you've partitioned them, into tens and ones.

So let's have a look at 45, 45 has been partitioned into one, two, three, four tens and one, two, three, four, five ones and 32 has been partitioned into one, two, three tens and one, two ones.

Notice I've also written it so it's 40 plus five and 30 plus two.

Now in order to work out what needs to go in this box here, the other part, I need to subtract this part away from our whole to see what we're left with.

So let's have a look at doing that together.

Again you can see 45 is written here, in our expanded method and here it's shown with our dienes.

So there's the four tens and the five ones and thirty-two there's the three tens and the two ones.

Again written here is thirty plus two and forty plus five.

Now we know I must start with my ones column so I'm going to take two ones away from my five ones, so imagine there's not those two here, I would be left with one, two, three ones.

There we go, one, two, three ones.

Now I need to take three tens away from four tens, so I'm going to count one, two, three tens, it leaves me with just my one ten.

So here I'm left with one ten and three ones, which is the same as saying 13.

It's also been written here as 10 because I know that 10 dienes represents 10 ones, plus three and I know 10 plus three is equal to 13.

Now it's time to have a look at today's talk task.

Here at talk task today I would like you to have a go at choosing an equation from these equations here, I have I'd like you to have a go at partitioning both of the numbers and using the expanded method to subtract them.

For example, I'm going to take the first number here.

First equation here, sorry.

54 subtract 31.

I've partitioned 54 into 50 and four and 31 into 30 and one.

I know I have to subtract my ones first so I'm going to do 4 subtract 1 equals 3.

I've got my 4 here, my 1 here and I know I'm subtracting so my equation is going to be four subtract one is equal to three.

Then I'm going to look at my tens, I've got my 50 here and my 30 here so I'm going to do 50 subtract 30 is equal to 20.

Then I must do something called recombining, I need to recombine my tens and my ones, I'm going to do 20 plus 3 is equal to 23.

Remember don't forget to say it out loud box here, pause the video now to have a go at today's talk task.

Welcome back, let's have a look at our developed learning today then.

So we're going to look at 54 subtract 31.

This time we've got it shown where it's in our tens and ones columns, Good, but I've only got 54 shown in here because I'm going to physically take away 31 from that so, I've got my 54 one, two, three, four, five tens.

I know that my ten's column and four ones one, two, three, four.

54.

I want to take away 31.

I partitioned 31 into tens and ones, I know I've got three tens and one one.

We know we start with our ones so let's take away one of those ones from our one.

We're left with three ones.

We need to move it down to here to show that it's in our equals two box, so we've taken away our ones.

Next thing we have to do then is look at our tens, we now need to take away our three tens, because we partitioned 31 into three tens and one one, which is going to leave us with two tens, one, two, we need to make sure they're in the correct box, which is down here, move it to that, leaves us with 23.

Let's have a look then what's happening when we are writing that out with numbers.

So we've got our 54, again is partitioned into five tens and four ones and we've got our 31 which is again partitioned into three tens and one one.

We always start with our ones columns, so we're going to start here.

Four subtract one is equal to three.

Five subtract three is equal to two.

We know that's not really five and three, we know those fives and three, the five and three represents tens, so we know that two actually represents twenty but we know because it's in the tens column, we don't have to write that out.

We know that that two represents two tens.

So our answer again is 23, the same as here but it just looks different because it's written out as numbers, not drawn out as dienes.

Okay you're ready for today's independent task.

Today's independent task, I'd like you to have a go at these equations here, you can use the grid here to help you.

Remember you can either draw out the dienes, use the expanded method or try the column method to solve the equations.

Choose which of the methods you would like to use or have a go at using different methods.

I want you to think, do you notice any patterns in the numbers and can you explain them? Please pause the video now to complete your task.

Welcome back, let's have a look then at today's answers.

I'm going to start here with 54 subtract 32 is equal to 22.

44 subtract 32 is equal to 12.

34 subtract 32 is equal to 2.

67 subtract 33 is equal to 34.

67 subtract 32 is equal to 35 and 67 subtract 31 is equal to 36.

Did you notice any of the patterns in the numbers and could you explain them? I've noticed that my tens in this column are decreasing by one ten each time in our answer because in our equation our number is decreasing by 10 each time.

I've noticed here our numbers are increasing by one in the ones column, 34, 35, 36.

They're increasing in the ones column in our answer but in our equation, they're decreasing in the ones column.

So we've spotted some patterns in our answers today.

Well done for working so hard today.

Please pause the video now to have about today's final quiz and I'll see you again soon.

Thank you, bye bye.