Lesson video

Hello there, my name is Mr. Goldie and welcome to today's maths lesson, I'm sure you're going to enjoy it.

And here is our lesson outcome.

I can add and subtract multiples of 100.

And here are the keywords for today's lesson.

So the first keywords are known facts, can you say known facts? And the second keyword is multiple.

Can you say multiple? Excellent! So a known fact is something that you already know and can use to help you.

You might know that 6 add 6 = 12.

You can use this known fact to calculate 60 + 60 = 120.

A multiple is the result of multiplying a number by another whole number.

So 10, 20, and 30 are all multiples of 10.

2, 4, 6, and 8 are all multiples of 2.

And here's our lesson out outline.

So our first part of the lesson is adding and subtracting multiples of 100.

And the second part of the lesson is adding and subtracting with 3 multiples of 100.

Let's get started.

In this lesson, you will meet Sofia and Andeep and they're going to be helping you with your learning today.

Andeep is adding and subtracting multiples of 100.

"What is 100 add 100?" Asks Andeep.

Here's 100.

"You can use known facts," says Sofia.

1 add 1 = 2 10 + 10 = 20.

100 add 100 = 200.

So 100 add 100 = 200." We could also represent that on a number line.

We can start on 100, add on 100, and we get the answer 200.

"What is 300 add 100?" Asks Andeep.

There's 300, and again, Sofia says, "You can use known facts.

3 add 1 = 3 30 add 10 = 40.

300 add 100 = 400." So there's our 300, we add 100 on, we get our answer 400.

And again, we could represent that on a number line as well.

So 300 add 100 = 400.

"What is 300 subtract 100?" Says Andeep.

There's 300.

And again, Sofia says, "You can use known facts.

So you probably know that 3 subtract 1 = 2.

30 subtract 10 = 20.

So 300 subtract 100 = 200." Let's start off with our 300.

We subtract 100, we're left with 200.

And again, we can represent that on a number line as well.

300 subtract 100 = 200.

What is 700 subtract 100?" Asks Andeep.

There's 700.

And again, Sofia says, "You can use known facts.

You probably know that 7 subtract 1 = 6, 1 less than 7 is 6.

70 subtract 10 = 60.

700 subtract 100 = 600." And there is our representation again, using our base 10 blocks.

We've got 700, we subtract 100, we are left with our answer 600.

And again, we can represent that on the number line.

700 subtract 100 = 600.

Sofia calculates the missing number in these equations.

So 200 add 100, and 200 Subtract 100.

So Sofia's gonna start with 200.

, she's going to add 100, gets the answer 300 200 subtract 100 would = 100 800 add 100, what would the answer be? So again, Sofia starts on 800, she adds 100, gets the answer 900.

800 subtract 100 would = 700.

And again, we could use know facts to work out the answers.

So you probably know that 8 add 1 = 9, and 8 subtract 1 = 7, and you could use those to work out those calculations.

Now here's a couple of calculations to try on your own.

Calculate the answers.

So you've got two questions there.

500 add 100, 500 subtract 100.

Can you work out the answers? And maybe think about the known facts you could use to help you work out the answers.

Pause the video and have a go at calculating those two answers.

And now, welcome back.

Hopefully, you got the answers.

So you should have worked out 500 add 100 as being 600.

And you might have known 5 add 1 = 6.

So 500 add 100 = 600, and 500 subtract 100 would = 400.

5 subtract 1 = 4 500 subtract 100 = 400.

Well done if you've got both those correct.

"What is 300 add 300?" Andeep is saying, "I know that 3 add 3 = 6." There's 3, add another 3 and that gives us the answer 6.

Sofia is saying, "I know that 30 add 30 = 60 3 tens add 3 tens equals 6 tens." That's three tens, add another three tens, that equals 6 tens or 60.

So what is 300 add 300? How do these known facts help you calculate 300 add 300? "3 hundreds add 3 hundreds equals 6 hundreds," says Andeep.

There's 3 hundreds, add another 3 hundreds, and that would equal 600, so 6 hundreds altogether.

3 add 3 equals six, 3 hundreds add 3 hundreds equals 6 hundreds.

Andeep also represents a problem using a number line.

So this time he starts on 300, and he counts on 300, he gets the answer 600.

What is 800 subtract 400? Andeep is saying, "I know that 8 subtract 4 = 4." Andeep probably knows that 4 add 4 = 8.

So 8 subtract 4 = 4.

There's 8, and we subtract 4 and we're left with 4.

8 subtract 4 = 4.

And Sofia is saying, "I know that 80 subtract 40 = 40.

8 tens subtract 4 tens equals 4 tens." And Sofia has represented 80 using base 10 blocks.

She subtracts 40 and she is left with 40 How do these known facts help you calculate 800 subtract 400? So what is 800 subtract 400? 8 hundreds subtract 4 hundreds equals 4 hundreds.

So Andeep has represented the 800 there.

800, we subtract 400, we are left with the answer 400.

Andeep also represents the problem using a number line.

And this time he starts on 800 and he counts back 400, and that gets the answer 400.

Sofia uses known facts to help her calculate with multiples of 100.

So we've got a table there and it says, "I can use.

." on one side, and the other side it says, "To help me calculate.

." So it says, "3 add 2 = 5." How could you use that to help you work out 300 add 200? And what that would equal? Well, 3 add 2 = 5 300 add 200 must = 500.

Let's look at the next one.

So the next one says, "6 subtract 2 = 4." What is 600 subtract 200? Well, if 6 subtract 2 = 4, 600 subtract 200 must = 400.

The next calculation says, "I can use 4 add 3," and you probably know that 4 add 3 = 7.

And you could have worked that out because that's a near double, isn't it? 4 add 4 = 8, so 4 add 3 must be one less, 4 add 3 = 7.

So 400 add 300 must = 700.

And the last calculation, 8 subtract 3.

Now you probably know 8 subtract 4 = 4.

So 8 subtract 3 must = 5.

So if 8 subtract 3 = 5, 800 subtract 300 must = 500.

What is 400 subtract 200? Andeep says, "I know that 4 subtract 2 = 2.

There's 4, we're going to subtract 2, that gets us the answer 2.

Sofia says, "I know that 40 subtract 20 = 20.

There's 40, we subtracted 20, we're left with 20.

So what is 400 subtract 200? Pause the video and work out the answer.

Welcome back, and let's see whether you were right.

So 400 subtract 200, what was the answer? 400 subtract 200 = 200.

There's 400, subtract 200 = 200.

Very well done if you use known facts to help you work out the answer, and now we're going to look at our task, so Task A.

The first part of Task A, can you complete the calculations? So you might want to use know facts to help you work out the answers.

And you can use the number line underneath, it's bound to help you or use base 10 blocks to help you.

Part 2, complete the number facts and use them to help you calculate with 100s numbers.

So think about filling in that, I can use.

part, and then what can it help you to calculate? And then Part 3 of Task A, how many ways can you complete these calculations using multiples of 100? So the first calculation says, "Something add something = 800,' and you've gotta to use multiples of a hundred to add up to make 800.

And the second one says, "Something subtract something = 200." And again, you've got to use multiples of 100.

How many different ways can you complete these calculations? So pause the video and have a go at Task A.

And welcome back, and let's look at those answers.

So here are the answer's for Part 1.

So 400 add 100 = 500, 4 add 1 = 5.

So 400 add 100 = 500, 400 subtract 100 = 300.

Well done if you've got those ones correct.

And the second part, using the know facts to help you calculate.

So we've got that 5 add 4 = 9.

So 500 add 400 = 900 9 subtract 4 = 5, so 900 subtract 400 = 500.

Well done if you've got those correct.

And here are the possible answers for Part 3.

So quite a few different answers, particularly for the number that subtracts from another to equal 200.

Hopefully, you found lots and lots of different ways of doing those.

So very, very well done on Task A.

And let's move on to Part 2 of the lesson.

So Part 2 of the lesson is adding and subtracting with three multiples of 100.

Sofia wants to find the missing sum from the bar model.

So we've got a bar model there with the numbers 200, 100, and 100 as parts.

"I need to add together 200 add 100 add 100," says Sofia.

So she's going to use the number line to help her work out the answer.

Sofia starts on 200 and adds 100.

So she adds 100, then she adds another 100.

200 add 100 add 100 = 400.

And that's her answer, 400, So the missing sum was 400.

Sofia wants to find the missing sum from this bar model.

"I need to add together 300 add 200 add 100," says Sofia.

So Sofia starts on 300 and adds 200.

And normally when we are adding numbers together, it's normally sensible to start with the bigger number and add on the smaller ones.

So Sofia's gonna start on 300 and add 200, 300 add 200 = 500, 3 add 2 = 5, 300 add 200 = 500.

Then she adds another 100.

500 add 100 = 600.

Andeep is saying, "I know that 3 add 2 add 1 = 6.

So 300 add 200 add 100 = 600." So Andeep could have used known facts to work out that answer, there's our answer, 600.

Find the missing sum from the bar model.

There's a bar model with the three parts underneath, and Sofia's given you a bit of helpful advice here.

"Add together 100 add 500 add 100," and you can use a number line to help you work out the answer.

Or if you'd rather use base 10 blocks, you can use those instead.

So pause the video, can you work out the answer? And welcome back.

Did you manage to get the answer? Let's I look to see whether you were right.

So start on 500 and add 100.

Remember, it's most sensible to start with that largest number, and 500 is definitely the largest number there.

So 500 add 100 = 600, then add another 100.

600 add 100 = 700.

Oh, and here's Andeep, Andeep is saying, "5 add 1 add 1 = 7.

So 500 add 100 add 100 = 700." So the missing sum was 700.

Well done if you got that as the answer.

Sofia wants to find the missing number from the bar model.

So this time, one of the parts is missing, one of the addends is missing.

"I can find the missing number by calculating 700 subtract 200 subtract 100," says Sofia." So Sofia's going to use the number line again, to help her work out thee answer.

Sofia subtracts 200 from 700.

So she starts from 700 and counts back 200.

That gets the answer 500.

Then she subtracts another 100.

So 500 subtract 100 = 400.

Oh, and Andeep is saying, "I know 7 subtract 2 subtract 1 = 4, 700 subtract 200 subtract 100 = 400." So again, Andeep is making good use of his known facts to help him work out the answers.

So the missing number is 400.

Sofia wants to find the missing number from this bar model.

So this time, we've got the sum of the top, 800, and we've got two of the parts as being 100 and 100.

Sofia says, "I can find the missing number by calculating 800 subtract 100 subtract 100." So again, Sofia can use her number line to help work out the answer.

She starts on 800 and she subtracts 100.

So 800 subtract 100 = 700.

Then she subtracts another 100.

700 subtract 100 = 600.

So the missing number must be 600.

And Andeep is again saying, "I can use know facts to work this out.

I know 8 subtract 1 subtract 1 = 6.

So therefore, 800 subtract 100 subtract 100 must = 600." So the missing number is 600.

Find the missing number from the bar model.

So we've got the sum at the top and we've got two of the parts.

How could you work out the missing part? And Sofia's giving you a bit of helpful advice here.

"Find the missing number by calculating 500 subtract 200 subtract 100.

And again, you can use a number line to work out the answer.

Or instead, if you prefer, you could use base 10 blocks.

So what is the missing number? Pause the video and have a go finding out the answer.

And welcome back and let's see how you got on.

So hopefully, you started with 500 and subtracted 200.

So 500 subtract 200 = 300, and then you subtracted another 100.

So 300 subtract 100 = 200.

And here's Andeep again.

And Andeep is saying, "I know 5 subtract 2 subtract 1 = 2, 500 subtract 200 subtract 100 = 200." Andeep is very good at his known facts and is very good at using them to help him work out other answers.

So the missing number is 200.

Very well done if you've got that as the answer.

Sofia and Andeep try to find the missing number.

300 plus something plus 300 = 800.

How could they work out the missing number? Sofia is saying, "I can use subtraction.

8 subtract 3 subtract 3 = 2.

So 800 subtract 300 subtract 300 = 200." Sofia is saying, "You could use subtraction to work out the answer." So we start from 800, we subtract 300, that gets us the answer 500, and then subtraction of the 300, and that gets us a missing number, 200.

Andeep is saying, "I can use addition.

I know 3 add 3 = 6.

300 add 300 = 600.

So 300 add 300 add 200 = 800." So Andeep starts on 300, he adds 300 on, and that gets him the answer 600, and then he just has to work out what else he has to add to get to the answer 800.

So 600 add another 200 = 800.

So the answer would be 200.

So two different methods for working out the answer.

Sofia wants to find the missing numbers from the bar model.

So this time, there are two missing numbers.

We've got the sum of the top 700, and one of the addends, one of the parts is 200.

What could the other parts be? I know 700 subtract 200 = 500," says Sofia.

"The two other addends add up to equal 500." So Sofia knows that the two parts add up to make 500.

Andeep thinks he has a solution.

"I know 3 add 2 = 5 So 300 add 200 = 500." So Andeep is saying, "That the other two parts could be 300 and 200." That's one possible solution.

Is there another way of doing it? Can you find a different answer? So find a different way of making the sum 700.

How else could you solve this problem? So the sum is 700, one of the parts is 200, what could the other two parts be? Pause the video and see if you can come up with a different answer.

And welcome back, let's see how you got on.

Here's another solution.

It's not the only other way of doing it, but it's another possible solution, and you may have come up with something very, very similar to this one.

So you could have had the numbers 400 and 100.

They also add up to make 500.

So 200 add 400 add 100 = 700.

That's another different possible answer.

Very well done if you've got that answer or a different one that also worked.

And let's move on to Task B.

The first part of Task B is you've got to find the sum.

So for each of the bar models, there are three parts.

You've got to add the parts together to find the sum at the top.

So in Part 2, you've got to find the missing number.

How could you find the missing part? And you could use known facts to help you work out the answer.

You could use addition, you could use subtraction.

You may want to use base 10 blocks to help you work out the answer or use the number line.

It is up to you what methods you would like to use.

And then Part 3, use multiples of 100 to complete the bar model.

So you've got to use multiples of 100.

How many different solutions can you find? How many different ways can you find of making that bar model correct? So one of the parts is 200, the sum is 900, what could the other parts be? Pause the video and have a go at Task B, and very best of luck.

And welcome back, and let's look at those answers, see how you got on.

So Part 1: Find the sum.

So 400 add 100 add 100 add up to make 600 300, 300, and 100, add up to equal 700.

So very well done if you've got those ones correct.

And here are the answers for Part 2, these are the missing numbers, the missing addends.

So for the first one, 800 was the sum, two of the parts were 200 and 200, and the missing part was 400.

So very well done if you've got those correct.

And let's move on to Part 3 So here are some possible answers for Part 3.

So each time the sum has got to be 900, and you're given one of the parts 200, so the other two parts must add up to have a sum of 700.

So you could have had 100 and 600, or 600 and 100, and you could have had 200 and 500, they also add up to make 700, or you could have had 500 and 200, 500 add 200 also = 700.

And if you add the other 200 on, you get sum 900.

So very well done if you came up with lots and lots of different ways of making 900.

So excellent work today, and I hope you're feeling much more confident with adding and subtracting using multiples of 100.

Brilliant work, very, very well done indeed! And let's look at our lesson summary.

So our lesson summary is, you can use known facts to help you calculate with multiples of 100, You can use 3 - 1 = 2 to help you work out 300 - 100.

You can use addition or subtraction to solve some problems..