Lesson video

Hello, my name's Mrs. Hopper, and I'm really looking forward to working with you on this lesson from our unit on reviewing column edition and subtraction.

Are you ready to work hard? Are you ready to remember perhaps some things that you've learned before? Well, if so, let's make a start.

So in this lesson, we're going to be using column subtraction, including regrouping from the hundreds to the tens.

We've got two key words, column subtraction and regroup.

So I'll take my turn, then it'll be your turn.

My turn, column subtraction.

Your turn.

My turn, regroup.

Your turn.

Well done.

They may well be words you're very familiar with.

Let's just remind ourselves what they mean.

They are important in the lesson.

Column subtraction is a way of subtracting numbers by writing a number below another, helping us to keep track of our subtractions and to work effectively and efficiently.

The process of unitizing and exchanging between place values is known as regrouping.

For example, 10 tens can be regrouped for 100.

100 can be regrouped for 10 tens.

And that's gonna be really important to us today we've got two parts to our lesson.

In the first part, we're going to be regrouping from hundreds to tens.

And in the second part, we're going to be regrouping from hundreds to tens and from tens to ones.

So let's make a start.

And we've got Alex and Lucas helping us in our lesson.

Alex is unsure how to calculate 215 subtract 133.

He says, "I really can't remember how to do this.

I wonder if you can." Could you help him out? Lucas says, "What's the problem Alex?" And Alex says, "The tens digit of the subtrahend is greater than the tens digit of the minuend." Let's remind ourselves what those words mean.

The subtrahend is the number we are subtracting.

So 133.

And the minuend is our whole, the number we're starting with, 215.

And the tens digit in 215 is smaller than the tens digit in 133.

So 110 subtract 310 would be difficult to do in our column subtraction.

Lucas says, "It's not a problem, you just need to regroup one of the hundreds as 10 tens." Ah, we know that 100 is equal to 10 tens.

So we can take one of those hundreds and regroup it as 10 tens and add them into the tens column.

Lucas says, "Let's start by representing 215 using base 10 blocks." So there they are.

2 hundreds, 1 ten, and 5 ones.

And from that we're going to subtract 133.

Let's start with the ones.

Five ones subtract three ones is equal to two ones.

So there we go.

We can see our three ones have faded out.

3 tens is greater than 1 ten.

We have to regroup one of the hundreds as 10 tens.

We haven't got enough tens on their own, but we've got lots of tens locked up in those hundreds.

So we've regrouped one of the hundreds into 10 tens.

There are now 11 tens and 11 tens subtract 3 tens is equal to 8 tens.

So we've got plenty of tens now.

We can subtract our 3 tens and we've got 8 tens remaining.

100 subtract 100 is equal to zero 'cause we've only got one whole hundred left and we need to take away one of the hundreds for the 133.

So our whole hundred has disappeared.

As Alex said, "215 subtract 133 is equal to 82.

That really helped, Lucas, thank you." He's going to use column subtraction to calculate 215, subtract 133 now.

Can you picture what was happening with the base 10 blocks maybe to help you? He says, "I need to start with the smallest place value first." 5 ones subtract 3 ones is equal to 2 ones.

The tens digit of the subtrahend is greater than the tens digit of the minuend.

Three is greater than one.

I'll regroup 100 as 10 tens.

So now there's 1 hundred and 11 tens.

11 tens subtract 3 tens is equal to 8 tens and 100 subtract 100 is equal to zero hundreds.

Well done, Alex.

215 subtract 133 is equal to 82.

And I hope you were picturing what was happening with the base 10 blocks as we were doing the crossings out and rewriting the numbers in the minuend of our calculation.

Over to you now.

You're going to look at each column subtraction.

Do they need regrouping in the tens? So you're going to focus in on those tens digits.

Can you spot whether they need regrouping? Is the tens digit of the subtrahend greater than the tens digit of the minuend? So pause the video, have a look, and we'll come back and talk through them together.

How did you get on? Yes, in the first one, regrouping is needed.

We've got 1 ten in our minuend and 4 tens in our subtrahend.

And regrouping is needed again for the middle one.

There are 6 tens in the minuend and 8 tens in the subtrahend that we're subtracting.

What about the last one? Nope, regrouping is not needed in the tens here.

We've got 3 tens and we're subtracting 3 tens.

We just won't have any tens.

Well done if you've got those right.

It's really useful to look carefully at the numbers in a column subtraction so that you can identify whether regrouping is going to be needed or not.

So Alex is using column subtraction to calculate 536 subtract 84.

He says, "I need to start with the numbers with the smallest place value." So he's gonna start with the ones.

6 ones subtract four ones is equal to two ones.

The tens digit of the subtrahend is greater than the tens digit of the minuend.

Eight is greater than three.

I'll regroup 100 into 10 tens.

So now there are 4 hundreds and 13 tens.

13 tens subtract 8 tens is equal to 5 tens and 4 hundreds subtract zero hundreds is equal to 4 hundreds.

536 subtract 84 is equal to 452.

You're getting really good at this, Lucas.

Over to you.

Can you use column subtraction to calculate 628 subtract 277? Alex says, "Start with the numbers with the smallest place value." So pause the video, have a go, and we'll look at the answer together.

How did you get on? So we started with the ones.

8 ones subtract 7 ones is equal to 1 one, but the tens digit of the subtrahend is greater than the tens digit of the minuend.

Seven is greater than two.

So we're going to regroup 100 as 10 tens.

So now there are 5 hundreds and there are 12 tens.

12 tens subtract 7 tens is equal to 5 tens and 5 hundreds subtract 2 hundreds is equal to 3 hundreds.

So 628 subtract 277 is equal to 351.

Time for you to do some more practise.

Complete each calculation using column subtraction and you will need to regroup from the hundreds to the tens.

So pause the video, have a go, and we'll look at the answers together.

How did you get on? So here are the answers to the first three.

So in A, we only had 3 tens in our minuend and we were subtracting 4 tens in the subtrahend.

So we regrouped one of the hundreds.

So we now have 2 hundreds and 13 tens.

And in B, we had to subtract 9 tens from seven.

So we had to regroup one of the hundreds.

So we had 3 hundreds and 17 tens.

And then in C, we were only subtracting a two digit number, but we still needed to regroup.

So we regrouped one of the hundreds.

So we had 4 hundreds and 15 tens so that we could do the subtraction.

And Alex is reminding us the tens digit of the subtrahend is greater than the tens digit of the minuend in all of these cases.

And for the second set, similar thinking.

But E was quite interesting.

The tens digit of the minuend is zero.

100 is regrouped into 10 tens, so that there are 10 tens in total.

So in E we regrouped to hundreds.

So there were six hundreds and 10 tens.

I hope you were successful with those and you've got your regrouping sorted out.

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

This time we're going to regroup from the hundreds to the tens and the tens to the ones.

So Alex is looking at this calculation.

What can you see? He says, "I'll need to regroup in the tens.

The tens digit of the subtrahend is greater than the tens digit of the minuend." Yup, that's right, Alex.

4 tens is greater than 2 tens.

There we are.

Have you spotted something else? Ah, Lucas has.

He says, "You'll also need to regroup in the ones." The ones digit of the subtrahend is greater than the ones digit of the minuend.

4 ones is greater than 2 ones.

So we've got a lot of regrouping to do here.

Alex uses column subtraction to calculate it.

He says, "First, I'll regroup 1 ten as 10 ones." So now there is 1 ten and there are 12 ones.

12 ones subtract 4 ones is equal to 8 ones.

I'll regroup 100 as 10 tens.

So now there are 4 hundreds and we had 1 ten left from our regrouping before and we've put 10 more in.

So now we've got 11 tens.

11 tens subtract 4 tens is equal to 7 tens and 4 hundreds subtract 2 hundreds is equal to 2 hundreds.

So 522 subtract 244 is equal to 278.

Alex is looking at this calculation.

He says, "I'll need to regroup the ones.

The ones digit of the subtrahend is greater than the ones digit of the minuend." That's right, nine is greater than six.

Lucas says, "Do you need to regroup in the tens as well?" Hmm, we've got zero tens.

Take away zero tens, it doesn't look like it.

He says, "I don't think so.

Zero tens subtract zero tens is equal to zero tens." So he is going to use his column subtraction to calculate.

606 subtract 209.

First, I need to regroup 1 ten as 10 ones.

But the tens digit of the minuend is zero.

Where's he going to get a 10 from? "Ah," he says, "I'll need to group 100 as 10 tens first." We know we've got tens, but they're locked away in our hundreds.

So he's going to regroup one of the hundreds.

So now there are 5 hundreds and there are 10 tens.

"Now," he says, "I can regroup 1 ten as 10 ones." So there are now 9 tens and there are 16 ones.

So we've regrouped a hundred for 10 tens, and then we can use those 10 tens to regroup one for 10 ones.

So now we can complete our column subtraction.

16 ones subtract 9 ones is equal to 7 ones.

9 tens subtract zero tens is equal to 9 tens and 5 hundreds subtract 2 hundreds is equal to 3 hundreds.

So 606 subtract 209 is equal to 397.

"You had to regroup in the ones and the tens," says Lucas.

You might want to have another look at that, have a go at it yourself, and make sure you can see why all that regrouping was needed so that we could have an extra 10 ones in our ones column.

So time for you to have a look.

Look at each calculation and explain how you will need to regroup in each case.

Will you need to regroup a 10 into 10 ones? And will you need to regroup a hundred into 10 tens? Or maybe you'll need to do both.

Look carefully at each calculation.

And Lucas is asking a question, do you need to regroup in the tens because you had to regroup a 10 as 10 ones? That might be something to look for.

Pause the video, have a look at the calculations, and we'll discuss your thinking afterwards.

How did you get on? So in this calculation, regrouping is only needed in the ones.

If we regroup one of those tens, we'll still have 5 tens and we can subtract three.

In this calculation, regrouping is needed in the ones and the tens.

In both cases, the digit in the subtrahend is bigger than the digit in the minuend.

What about the final one? Well, regrouping is needed in the tens here because regrouping is also needed in the ones.

So if we regroup one of the tens to give us 12 ones, we'll then only have 6 tens.

So we will need to regroup a hundred into 10 tens so that we can complete the subtraction of the tens.

Really useful to look carefully at the numbers before you start doing your calculation just to make sure that you've spotted when regrouping is going to be needed.

Alex has these number cards.

He says, "Choose three of the cards and make a three-digit number." So Alex says, "I'll make the number 954." Lucas says, "Now reverse the digits to get another three-digit number." He says, "That gives me the number 459." So 954, reverse the order of the digits, 459.

Lucas says, "Now subtract the smaller number from the larger number." So Alex says, "Let's calculate 954, subtract 459." Can you see if you'll need to do any regrouping? You're going to have a go.

Can you complete the calculation for Alex? He says, "Start with the numbers with the smallest place value." Do you think you're gonna need to do any regrouping? Pause the video and have a go and then we'll talk through your answer together.

How did you get on? Alex says, "We need to regroup 1 ten as 10 ones." So now there are 4 tens and 14 ones.

14 ones subtract 9 ones is equal to 5 ones.

Ah, and this is one of those cases where we now need to regroup in the hundreds to the tens as well.

We need to regroup 100 as 10 tens.

So now there are 8 hundreds and 14 tens.

14 tens subtract 5 tens is equal to 9 tens and then 8 hundreds subtract 4 hundreds is equal to 4 hundreds.

So 954 subtract 459 is equal to 495.

Time for you to do some practise.

You're going to complete each column subtraction and think carefully about whether you need to do any regrouping.

And for part two, and you're going to play Lucas's game.

You're going to use these number cards.

Choose three of the number cards and make a three digit number.

So we've got 327.

Now, reverse the digits and get another three-digit number.

723.

Next, subtract the smaller number from the larger number.

So here we do 723 subtract 327, and we'll use a column subtraction to do it.

Lucas says, "Do this a few times.

Do you notice anything?" Pause the video, have a go at your tasks, and we'll get together for some feedback.

How did you get on? Here are the answers for one.

So we had a lot of regrouping to do, didn't we? In the first two, we knew we were going to have to regroup from the tens to the ones and from the hundreds to the tens.

And in C, we had to regroup from the hundreds to the tens because we had to regroup from the tens to the ones.

So Lucas says, "Each column subtraction needed regrouping in the ones and the tens." How did you get on with two? Here are some possible answers you might have got.

So we had 413 subtract 314.

So lots of regrouping needed there to get an answer of 99.

And again, lots of regrouping needed here to get an answer of 396.

Did you do this a few times? Did you notice anything? So you may have noticed Alex says that you kept getting the same differences.

99, 198, 297, 396 perhaps.

Ah, Lucas spotted something.

When you add the digits of the difference, you always get 18.

So nine add nine is equal to 18, and nine add three add six is equal to 18 here.

So you always get a digit sum, we call it, of 18.

I wonder why that happens.

I hope you enjoyed having a go.

Maybe you could try this task out on somebody else, a friend, or maybe somebody at home.

And we've come to the end of our lesson.

So I hope you've enjoyed reviewing, using column subtraction with regrouping from hundreds to tens.

It may be something you've done before and you've reminded yourself about it, or it may be something new.

So what have we learned about? We've learned that we need to regroup when the ones or tens digit of the subtrahend is greater than the ones or the tens digit of the minuend.

So we are subtracting a larger value digit than the value of the digit in our whole.

We can regroup a 10 into 10 ones and we can regroup a hundred into 10 tens.

And we've also learned that if the tens digit of the minuend is a zero, you need to regroup the hundreds before you can regroup the tens.

And that's a really useful strategy to have ready.

Thank you for all your hard work today.

I hope you've enjoyed it, and I hope I get to work with you again soon.

Bye-bye.