Lesson video

Hello and welcome to today's session we're carrying on the unit exploring calculation strategies.

And today's objective will be to subtract to two digit numbers, which require regrouping by using the column method.

Let's get started.

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.

So I thought I'd start today with a little riddle.

How can a leopard change its spots? The thing how can a leopard changes its spots by moving from one spot to another, let's get started then.

So our agenda for today's lesson.

As I said, we're going to be learning how to use the column method for subtracting two two digit numbers that require a grouping together.

First of all, we'll start with a quiz to test your knowledge.

Then we'll look at today star words, we're going to look at partitioning and pictorial models.

It'll be time for you to do your talk task.

And then we're going to look at how we can use the column method both with dienes and with written numbers.

Then you'll be ready for your independent task and we'll review the answers together.

And finally, there'll be a quiz to see what you've remembered.

Please pause the video now to complete your starter quiz.

Welcome back, let's have a go then at today's star words we're going to do them using my turn your turn, place value tens ones column regroup subtract is equal to fantastic let's get started then.

So we're going to look at this is our new learning today.

We've got 40 subtract 18 you can see here on our place value grid We've got 40 represented with four tens, Dienes one, two, three, four My question to you is, how can we use the column method to solve this? Can we subtract the tens first, but you'd have five seconds thinking about that question.

Okay, let's find out, how can we subtract the tens first, I want to take away 18 from 40.

So I'm going to subtract one out of 10.

One group of 10 from 40 is gives me three groups of 10.

Okay, now I need to subtract eight ones from my ones out there.

I don't have any ones here to subtract it from.

I've already gone wrong care.

So it's going to be really important when we're looking at our subtractions that we always start with our ones column.

So let's start afresh and look at the equation again, this time we're going to be starting with our ones.

Now, those of you that have noticed there is no one's in the ones column at the moment because I've got four tens.

But I've noticed that today when we're subtracting, we're going to have to do something a little bit different.

That's where I star words the word regroup comes in really handy.

So we need to regroup one group of 10 from our 40, to 10 ones into here, then we'll be able to subtract eight from those at the moment, we can't subtract eight because there is nothing to subtract it from.

So let's regroup one group of 10 to give us three groups of 10 for 10 ones, there they are, let's check.

Count with me one, two, three, four, five, six, seven, eight, nine, ten 10 ones is still representing 40 in total here, it's just we partitioned it slightly differently, so that we can now subtract our eight ones.

Let's have a look there eight of these away.

It's going to leave us with two, I know that my two has to go into my answer box, so I need to move them down into my answer box.

So I've subtracted my one so far.

The next thing we must do then is subtract our 10s.

So this time I need to take one group of 10 away from my three tens that are here.

I take one away, I'm left with one two see, there we go, there's our two and we know we have to move it down into our answer box.

So here's it.

This number now represents two tens and two ones, my number would be 20 to check perfect 22 now Now, today is on this place grid.

Here we're going to see what happens when we look at it with numbers.

So, again, we've got 40 partitioned into four tens and zero ones this time, we have got our other a number from our subtraction equation underneath this.

So we've got 18, partitioned into one tens, and eight ones.

Again, though, you'll notice, we cannot, at the moment, take our eight away from nothing.

We've got anything that we can take away from.

So just like we did over here, we're going to have to regroup one of our fours, one of our four tens but three tens.

Okay, and 10 ones here.

Now we can take eight away from 10.

And that I know that eight that sorry, I know that 10 subtract eight is equal to two.

So I can put two in here, and I can now do three, subtract one, which is also equal to two.

I know that that three and that one actually represents three tens and one tens.

And the two is actually representing two tens.

So my number would be 22, just the same as it was here.

Just looks a little bit different, because we've got both of the numbers in our boxes.

Let's have a look at another example.

This D subtract 12 have a think what do I have to do first? Well done to those of you that noticed, I can't take two away from no one's here.

So the first thing that I have to do, starting with my ones column, is I have to regroup one group of 10 for 10 ones from my 50.

So that's going to become four tens and 10 one's fantastic.

Now I can take away two from my one's here.

So imagine if I've got 10 ones here.

I'm going to take two of them away.

Imagine they're not here.

I would have one, three four, five, six, seven, eight, let's see.

There we go, there we go one, two, three, four, five, six seven, eight so I've been left with eight ones, we know they have to come down into this box here.

So let's put them where they belong, perfect.

Now I can subtract my 10s, I need to subtract one group of 10 from my remaining four groups of 10.

Okay, imagine we've taken this one away, we're left with one two three groups of 10.

And we know again that they have to come down into this box here, so let's put them into the correct box.

There we go, let's have a look at our number then.

If we recombine it we've got three tens.

So 30, and eight ones, so our answer would be 38.

And again, we're going to look at it where we have it with our written numbers, not just adding, so let's say we have 50 partitioned into five tens and zero ones, and 12 partitioned into one tens and two ones.

We know we have to start with our ones column.

And we know we cannot do zero, subtract two.

So we have to do some regrouping here.

So we're going to regroup one group of 10, which will leave us with four tens.

But 10 ones, just like we did over here.

Now I can do that I can do ten subtract two I know 10 subtract two is equal to eight.

So I'm going to add eight and my answer box.

Now I can answer my 10s column and each do four, subtract one is equal to three.

Again, you can see here, I know that three is three tens, because it's in my 10s column ,so my number is 38.

The same as the number here are shown differently.

This is shown without Dienes.

This is shown with our numbers.

Let's have a look at your talk task today.

Using Dienes or pictures of Dienes, I'd like you to complete the following equations.

You've got two equations here and you've got a plus five grid head to help you don't forget you can use to say out loud something ones or 10s subtract something ones or 10s is equal to this number has 10s and ones I will regroup 110 for 10 ones.

Pause the video now to have a go at today's top task.

Welcome back to what we're going to do now have a look at the develop learning today.

So, develop learning 41 subtract 16 is equal to got shown here and Dienes the number 41.

I want you to have five seconds thinking time to consider this question.

What is different to before? Well done to those of you that spotted this time I've got one in my ones box.

It's not zero.

If I look here at 41, this number here isn't zero.

So that's what's different, but the same, I know that six is greater than one.

At the moment, I haven't got six ones that I could take away here.

So again, I'm going to have to use my regrouping.

This time, there's not going to be just 10 ones here because I've already got one one here.

So this one's going to stay where it is.

We're not going to look at this one for the moment, we are going to regroup one group of our 10s so this 10 here is going to become 10 ones.

So I'm left with three tens and again 10 ones.

I still keep my one one here so in total, I should have 11 would like you to count with me and see if I have 11 ones one two three four five six seven eight nine 10 11 absolutely.

I still have my warm up, so I've got 11 ones, I need to take away six of those.

So I'm going to imagine I take away one two three four five six or leave me with five ones and count them one two three four five perfect.

I need to move those into my answer box now.

Let's move them down here.

I'm into our ones box.

Now I can start sorry, I can next carry on with my 10s.

I have got four tens but I regrouped once I've got three remaining, and I'd like to take away one group of those 10s I know that three, a great one is going to leave me with one two check, okay, and I know that I have to move that into the correct box.

So now I have two tens I know that's the same as saying 20 and five ones same as saying 25 my answer is 25.

Let's look then at what happens when I write it down as numbers.

Again, I've got 41, partitioned into four tens, and one one, and 16 partitioned into one tens and six ones.

There, I can see really clearly that I don't have six I've got to take away from I've only got one to take away from.

So again, I'm going to regroup one group of my tens for 10 ones.

So my 10s are going to become there's going to be three of them remaining, because I'm going to have 10 ones over here.

I have got one sale here because my number was 41.

So now I've got 11 ones to subtract my six from I know they're levels subtract six is equal to five.

So I can put five here the same as here.

Now I can do my 10s column, I've got three tens and I would like to take one of them away, and I will be left with two tens my number would be 25 the same as my number here.

So my answer is 25.

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

Today, I would like you to solve the following equations using using Dienes, pictures of Dienes, or the column method.

Remember to start with the ones column.

Pause the video now to complete your task.

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

So we're going to go through one question at a time and see how we adapt to it.

Looking at this question first, I can see I have to start with the ones column.

I've got two and I would like to take away six from it.

I know I need to do some regrouping.

So my six tenths becomes five tens.

I add 10 ones to here, my existing two which gives me 12 ones 12 subtract six is equal to six.

Five take away one is equal to four.

Now I know they 10s because they're my 10s column.

So I know my number is 46.

Next, then six, subtract nine, I can't do that, because I'm taking away a number that's greater than this number.

So again, I need to do some regrouping, my seven tens is going to become six tens.

And my six ones are going to become 16 ones, because the six ones still stay there.

And I've regrouped one tens for 10 ones 16 takeaway nine, I can do that.

And it gives me seven six tens take away three tens is equal to three tens.

So my answer would be 37.

In the habit to subtract seven, I know I can't do that because this number is greater than this number.

So I need to do some regrouping, my six tens are going to become five tens.

And I'm going to regroup one group of 10 for 10 ones, and I've still got my two so I've got 12 ones remaining.

Five, subtract seven is equal to five.

Now I can do five, subtract one is equal to four.

Remembering that those represent 10s.

So it's really 50, subtract 10 is equal to 40.

So my answer would be 45.

And come down here now to this equation, three subtract eight, I know that I can't do that without regrouping.

So I need to regroup one regroup of my six tens So I'm left with five tens and 10 ones, my two remains here, because I still had to do in 60.

So I've got 12 ones, and I want to subtract eight ones from it, which is going to give me four then I'm going to do five, subtract ten.

Sorry, 350, subtract 10, which is equal to 40 in my 10s column, so my answer is 44.

Next, then, I've got four ones, and I'd like to take away nine of them, I know I need to do some regrouping.

So my seven tens is going to become six tens, and I'm going to have 10 ones include and then I also have my four ones remaining.

So I have 14 ones in total, I'd like to take away nine of them just going to leave me with five, then I can do six tens take away three tens is equal three times my number is 35.

And last but not least, I have five ones.

And I'd like to take away nine, I have to do some regrouping again, I need to regroup seven tens the six tens and 10 ones, remembering I still have my five ones there.

So I have 15 ones in total 15 ones subtract nine ones is going to give me six ones.

Six, subtract three is equal to three remembering now in my 10s column, so I know they represent 10s my number would be 36.

Well, done worked really, really hard today with those questions.

Please pause the video now to have the final quiz and answer the final few questions.

See you again soon.

Thank you and goodbye.