Lesson video

Hello everyone, welcome back to another maths lesson with me, Mrs. Pochciol.

As always, I can't wait to learn lots of new things, and hopefully have lots of fun.

So let's get started.

This lesson is called calculate the difference, in different contexts.

And it comes from the unit calculating within 20.

By the end of this lesson, you should be able to calculate the difference, in different contexts.

Let's have a look at this lesson's key words.

Difference, subtraction and count on.

Let's practise, my turn difference.

Your turn.

My turn, subtraction.

Your turn.

My turn, count on.

Your turn.

Wonderful.

Now that we've said them, let's use them.

Let's have a look at our lesson outline.

In the first part of our learning, we're going to explore strategies to calculate difference.

And in the second part of our learning.

We're going to calculate difference, in different contexts.

Let's get started with the first part of our learning.

Exploring strategies to calculate difference.

In this lesson you are going to meet Andeep and Laura.

They're going to continue to help us with our learning today.

Laura wants to buy a birthday present for Andeep.

But she can't work out how much more the plane costs than the rockets.

It's very kind of Laura to spend her pocket money on Andeep, isn't it? So let's work out then.

How much more does the plane cost than the rocket? To find out, how much more the aeroplane costs than the rocket.

Laura is going to have to calculate the difference between them.

We can calculate the difference using subtraction.

So we need to calculate six, the price of the aeroplane, and four, the price of the rocket.

Six subtract four will give her the difference.

We know that six subtract four is equal to two.

The difference between six and four is two.

So the aeroplane costs two pound more than the rocket.

Well done if you spotted that.

Laura now reflects on her calculation.

We use subtraction, but because the numbers are closed together, we could have actually just counted on, to find the difference.

We can start with the part and count on, until we reach the whole number.

The larger number.

Start on four, and we know that two more is six.

So the difference between six and four is two.

We can use a counting on strategy, to find the difference of numbers that are close together.

So let's have a practise of this.

What is the difference between five and eight? Use accounting on strategy, and a number line help you.

Pause this video, find me the difference between five and eight.

And then come on back once you're ready, to see how you got on.

Welcome back.

Come on then Laura, how did you find the difference using our counting on strategy? Laura will start on five, and count on three more to eight.

Because she counted on three more.

She knows that the difference between five and eight must be three.

Well done to you, if you spotted that.

Andeep now tries using the counting on method, to find the difference here.

Is Andeep correct? He thinks that the difference between six and nine, is four.

Pause this video and have a think.

Come on back when you think you can decide whether Andeep is correct or not.

Welcome back.

I hope you enjoyed exploring Andeep's strategy there.

So is Andeep correct? Laura, what do you think? Let me check.

We're going to start at six, three more is nine.

Oh, Laura only counted on three more.

So she thinks that the difference between six and nine is three, not four.

Oh, Andeep has realised what he did wrong there.

He included six in his count, so he counted one too many.

That's where he got the four from.

So just be extra careful Andeep, when you are counting on in future.

We don't include the number that we start on.

Laura now notices some other things that Andeep would love for his birthday.

She wants to know how much more does the helicopter cost than the car.

Laura now solves this problem.

The car costs eight pounds.

The helicopter costs 13 pounds.

We notice that we have a number larger than ten.

So will Laura's strategy, of finding the difference still work? Let's have a look.

Let's try.

We're going to start at eight, five more is 13.

We counted on five more.

So Laura thinks that the difference is five.

It is.

Well done Laura.

The helicopter costs five pound more than the car.

A good strategy there, and it does work even if we use numbers larger than ten.

Well done Laura.

Laura now narrows it down to these two toys.

It's either the rockets, or the helicopter, that Andeep is going to get for his birthday.

But how much more does the helicopter cost than the rocket? Four and 13 are quite far apart.

So counting on, probably won't be your best strategy here Laura.

So she's going to calculate the difference using subtraction.

I think that's a good idea Laura.

So let's have a look.

The helicopter costs 13 and the rocket costs four.

So 13 subtract four.

Laura notices that she's going to bridge through ten here.

And we know how to do that don't we Laura? 13 subtract three is equal to ten.

Then ten subtract one is equal to nine.

So we know that the difference must be nine.

The difference between four and 13 is nine.

So we know that the helicopter costs nine pounds, more than the rocket.

That's a big difference there, isn't it? Laura wants to check her working.

Although counting on wasn't the best strategy to solve this problem, we can use counting on to check that our calculation is correct.

Laura will start on nine.

And if the difference between nine and 13 is four, then she's correct.

Ten, 11, 12, 13.

Yes, she counted on four more.

So nine is the difference between four and 13.

Well done Laura, some really good calculating there.

And I love how you used your counting on strategy, to check your working.

Over to you then, calculate the difference between these amounts.

What strategy will be best for you to use here? Did you use subtraction, counting on? Or something else to help you? So pause this video, find the difference in A, B and C.

But also think about what strategy, you use to find the answer.

Pause this video and come on back once you've had a go at all three questions.

See you soon.

Welcome back, I hope you enjoyed finding the difference there.

Did you manage to use all of those strategies for each of the questions? A, let's have a look at A then.

The difference between 12 and four is? Laura used subtraction here.

She noticed that she had to bridge ten.

12 subtract two is equal to ten.

Subtract two more, is equal to eight.

So the difference between 12 and four is eight.

And the best strategy to use there, was subtraction.

Well done if you found that eight was the difference.

Let's have a look at B then Laura.

How did you solve B? We use the counting on method here, because the numbers are quite close together.

Starting at 16, 17, 18, 19.

The difference is three.

So we know that 16, three more is 19.

The difference must be three.

Well done if you spotted this.

Which strategy did you use for C then Laura? Oh, for C Laura didn't use any of our strategies.

She just knew her number pairs to ten.

So we know that the difference between ten and six, is four.

Because six add four is ten.

Well done if you manage to find the difference, for all three of those problems. Let's move on then to task A.

For task A we're going to play a game, that's going to help us to calculate the difference between two numbers.

You're going to have a set of number cards.

We're gonna turn over two cards.

Laura returns over 16 and five.

She's going to find the difference now between 16, and five.

She's going to use what she thinks is the best strategy, to find the difference.

In this case, she's going to use subtraction.

16 subtract five.

We know that this isn't going to bridge ten.

So we can subtract five from the ones.

Six subtract five is equal to one.

And one, ten and one, one is equal to 11.

So she turned over the two cards.

Thought about the strategy.

Used the strategy to find the difference.

Laura now knows that the difference between 16, and five is 11.

Well done.

Pause this video.

Have a go at this game for yourself and come on back, once you're finished playing.

Then we can see how Andeep gets on, on his turn.

Welcome back.

I hope you enjoyed playing that game, and had lots of opportunities to practise finding the difference.

Shall we see how Andeep got on with his turn.

Come on then Andeep, what are you going to turn over? 13 and ten.

Hmm, let's see.

Andeep thinks he's going to count on, to find the difference between these numbers.

We start at ten, three more is 13.

We counted on three more.

So the difference between ten and 13 is three.

Laura suggested that she didn't need to count on, because she can see that 13 has three more ones than ten.

That would've been an even more efficient strategy.

Well done Laura, and well done Andeep.

I hope you enjoyed playing this game, and are feeling a lot more confident at finding the difference.

So let's move on to the second part of our learning.

Calculating difference, in different contexts.

Laura and Andeep now want to explore where else calculating the difference will be useful.

Andeep explains, that he had to calculate the difference last night.

When he was comparing his money with his sister's money.

Andeep had 11 pounds, and his sister had seven pounds.

So how did you calculate the difference then Andeep? Andeep had 11 pounds and his sister had seven pounds.

So how much more money does Andeep have than his sister? We can see 11.

The larger number as the whole.

And seven as the part.

The difference between them will tell us how much more money Andeep has than his sister.

They're quite close together.

So Andeep decides to count on from seven to 11.

We start on seven, four more is 11.

He counted on four more.

So he knows that the difference is four.

Andeep then found out that he had four pounds more than his sister.

Wow, I wonder what you're going to spend that money on Andeep.

Laura explained that she explored difference when she was looking at how the temperature changed throughout the day.

We recorded the temperature at the start of the day, and at the end of the day.

The morning temperature was 18 degrees, and the afternoon temperature was nine degrees.

They wanted to find out, how much the temperature had dropped over the day.

So how did you work this one out then Laura? We can see 18 the larger number as the whole, and nine as the part.

We can see this bar model being created again.

To calculate the difference, we can subtract the part from the whole.

So 18 subtract nine, will give us the difference.

Laura notices that this calculation will bridge ten, because nine ones is larger than eight ones.

So let's bridge ten then Laura.

18 subtract the eight first will give us 10.

Then 10 subtract one, the other part will give us nine.

So we know that the difference between 18 and nine is nine.

Well done Laura.

So that means that the temperature must have dropped, nine degrees during the day.

Wait, Laura's noticed something.

Double nine is equal to 18.

So we can say that the temperature dropped by half.

Wow, I love how you are using the other facts that you know here and bringing it into your maths.

Well done Laura.

Andeep now recalls another time, that he found the difference.

Last week Andeep was looking at his sunflower.

It measured 17 centimetres.

The difference in height now is two centimetres.

It's two centimetres taller.

What is the height of Andeep sunflower now? Come on then Andeep, how are you going to work that out? We know that the new height of the sunflower, will be our whole because we don't know what that is yet.

We know that the previous height of the sunflower will be the part, 17.

And we know that the difference is two centimetres, because that's how much it's grown by.

So to find the whole, we are going to add together the two parts.

17 plus two, will equal the whole.

17 plus two, is equal to 19.

So the new sunflower must measure 19 centimetres.

Wow, that's a really tall sunflower Andeep.

Well done to you.

Okay then, do you think you can help Laura work out, what her sunflower now measures? Last week, Laura's sunflower measured 16 centimetres.

But the difference in height now is three centimetres.

Her sunflower is three centimetres taller.

What is the height of Laura's sunflower now? You might want to use a bar model like Andeep did, to work out how tall his sunflower was.

Pause this video and have a go at calculating, how tall Laura's sunflower is now.

Come on back when you think you know the height of her sunflower.

Welcome back.

Come on then, I'm really eager to find out if Laura's summerflower is taller than Andeep's or not.

So 16 centimetres is the height that it was, last time Laura measured it.

We know that the difference is now three centimetres.

Her summerflower is three centimetres taller.

Three more than 16 is 19.

Andeep thinks that Laura's sunflower is 19 centimetres tall.

What do you think Laura? Laura knows that the difference between 16 and 19, is three.

So her sunflower is 19 centimetres tall.

Wow, some really tall sunflowers growing in the oak class.

Well done to you.

And well done to you if you worked out that Laura's sunflower was 19 centimetres tall.

Let's move on to task B.

Task B is to represent these problems as bar models, and calculate the difference.

Just like we've been doing with Laura and Andeep, during this learning cycle.

A, it takes Andeep 15 minutes to walk to school.

It takes Laura seven minutes to walk to school.

How much longer does it take Andeep to walk to school than Laura? B, Laura wants to buy a new pencil case that costs 14 pounds.

She has saved nine pounds so far.

How much more money does Laura need to save? And C when playing a game? The difference between Andeep score, and Laura's score is six.

Andeep scored eight.

So how many points could Laura have scored? Have a think about this one, because there might be more than one answer.

Pause this video, have a go at calculating those three word problems, and come on back when you're ready to find out how you've got on.

Welcome back.

Let's have a look then, at how Andeep and Laura solve these problems. It takes Andeep 15 minutes to walk to school, and Laura, seven minutes to walk to school.

So Andeep represents this using a bar model.

If we subtract seven from 15, that will tell us how much longer it takes Andeep to walk to school.

15 subtract seven, will bridge ten.

So let's do that.

15 subtract five is equal to ten.

And ten subtract two, is equal to eight.

The difference between 15 and seven, is eight.

So Andeep takes eight minutes more, than Laura to walk to school.

I think that that's because Andeep lives a little bit further away, rather than in walking a lot slower though.

What do you think? Let's have a look at B then.

Laura wants to buy a new pencil case that costs 14 pounds.

She has saved nine pounds so far.

Let's show this as a bar model then Laura.

We know that we've got nine pounds so far, but we need 14.

So the difference between 14 and nine, will be how much more money Laura needs.

14 subtract nine, will also bridge ten.

14 subtract four, is equal to ten.

And 10 subtract five, is equal to five.

The difference between 14 and nine, is five.

So Laura needs to save five pounds more, before she can buy the pencil case.

Come on Laura, I think you can do it.

Well done to you if you managed to work out, that it was five pound more that she needed.

And let's have a look at C.

When playing a game, the difference between Andeep score, and Laura's score is six.

So here we know the difference.

We know what Andeep score was.

That was eight.

So how are we gonna work this out then Andeep? It doesn't say if Laura has scored more points, or fewer points.

So there could be two possible answers here.

We know the difference is six.

So she could have scored six more points.

Which would be eight plus six, which we know is equal to 14.

So Laura might have scored 14 points.

What else could she have scored Andeep? We also know that she could have scored six fewer points, which would be eight subtract six.

Which we know has a difference of two.

Laura could have scored 14 points or two points.

Well done to you, if you found either of those, or are super well done if you managed to find both possible answers.

Well done for completing Task B.

Let's have a look at what we've covered today.

You calculate the difference by counting on, from the known part to the whole.

The difference is the answer to a subtraction calculation.

The difference is one of the parts that make the whole.

Thank you again for all of your hard work.

Enjoy the rest of your learning.

I can't wait to see you again soon.

Goodbye.