Lesson video

Hello, I'm Miss Cayley and I'm going to help you with today's lesson.

So today we're going to add and subtract multiples of 10.

So let's have a look at today's lesson outcome.

Here's the outcome of today's lesson.

I can add and subtract multiples of 10 to or from a multiple of 10.

Here are the key words for today's lesson.

Can you repeat them after me? My turn, add, your turn? My turn, subtract, your turn? My turn, multiple of 10, your turn? Well done, you might have seen these words before.

Look out for them in today's lesson.

Here's today's lesson outline.

First of all, we will add and subtract multiples of 10.

And then, we'll be looking at missing number problems. So let's start with the lesson.

In this lesson, you will meet Andeep and Izzy.

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

Andeep and Izzy have some pencils.

Can you see they've got some pencils in packs of 10? How many do they have altogether? Andeep said, "I have three packs of 10 pencils." Can you see his three packs of pencils? Izzy said, "I have two packs of 10 pencils." Can you see Izzy's pencils there? How many have they got altogether? Can you think of a known fact that can help us work it out? Andeep said, "I know that 3 plus 2 is equal to 5 so 3 tens plus 2 tens is equal to 5 tens." Is that what you thought? So 30 plus 20 is equal to 50.

We have 50 pencils in total.

Pencils can be represented on a bar model.

So here we've got 3 tens plus 2 tens and that's equal to 5 tens.

And here's the bar model to represent the pencils.

5 tens is the whole, 3 tens is a part, and 2 tens is a part.

3 tens is equal to 30 and 2 tens is equal to 20.

So 30 plus 20 is equal to 50.

So here's the bar model again with 50 as the whole and 30 is a part and 20 is a part.

Can you see that 30 plus 20 is equal to 50, and also 20 plus 30 is equal to 50? Let's check your understanding.

Which of these statements are correct? So here we've got a picture of the three packs of 10 pencils and two packs of 10 pencils and we've got some statements.

I want you to think about which ones are correct.

So the first one says 3 boxes plus 2 boxes equals 5 boxes.

Then it says 3 tens plus 2 tens is equal to 5 tens.

30 plus 20 is equal to 50.

There are 50 pencils altogether.

30 plus 20 is equal to 50.

There are 5 tens in total.

So pause the video and think about which of these statements are correct.

Which statements do you think were correct? Well, the first one is correct.

3 boxes plus 2 boxes is equal to 5 boxes.

So we've got 3 boxes of 10 pencils and 2 boxes of 10 pencils and that makes 5 boxes.

Then, we've got 3 tens plus 2 tens is equal to 5 tens.

That's true as well.

I can see we've got 3 tens plus 2 tens and that makes 5 tens.

30 plus 20 is equal to 50.

That's correct as well.

I can see we've got 30 pencils, and then 20 more pencils, and that makes 50 pencils.

There are 50 pencils altogether.

That's true as well.

30 plus 20 is equal to 50.

That's correct as well.

And there are 5 tens in total.

So all of the statements were correct.

Is that what you thought? Why are all the statements correct? Izzy said, "The boxes are in tens.

So 3 boxes and 3 tens mean the same thing." She said, "The total of pencils is 50 which can also be written as 5 tens." She said this symbol means plus.

So all of the statements were correct.

This is 1 ten.

Can you see Andeep and Izzy have got one group of ten cubes? And they've represented it on a place value chart.

It's showing that there is 1 ten and no ones.

How many more tens are needed to make 3 tens? You could try this with some cubes or other objects if you've got them.

Andeep said, "We need 2 more tens." So there we've got 2 more tens and that makes 3 tens in total.

2 tens is 20, so we've got 20 more cubes.

I wonder how it's going to look on the place value chart.

So now we have 3 tens.

We can see it on the place value chart.

So I wonder what's going to change on the place value chart.

We did have 1 ten and now we've got 3 tens.

The ones have stayed the same.

We've still got zero ones.

So the 3 represents the number of tens.

The tens digit increases by 2 when we add 2 tens.

Andeep said, "I know that 2 more than 1 is 3." "So 20 more than 10 is 30." What do you notice here? Can you see we've got 2 ones and 2 tens? Andeep said, "I know that 2 plus 2 is equal to 4 so 2 ones plus another 2 ones is equal to 4 ones." Izzy said, "So 20 plus 20 is equal to 40 so we've got 2 tens and we're going to add another 2 tens." So we're going to add 20 more and that makes 4 tens.

If 2 ones plus 2 ones is equal to 4 ones, then 20 plus 20 is equal to 40 because 20 is 2 tens and we're going to add another 2 tens and that will make 4 tens, that's 40.

This is 4 tens.

Can you see that Andeep and Izzy have made 4 tens out of cubes? And they've represented it on a place value chart.

We've got 4 tens and zero ones.

How many fewer tens are needed to make 2 tens? So how many tens do we need to subtract to leave 2 tens? Andeep said, "We need two fewer tens." So we've got 20 less cubes and we are left with 2 tens.

Izzy said, "Now we have 2 tens." We can see it on the place value chart.

So we did have 4 tens and now we've got 2 tens.

What happened to the tens digit on the place value chart? The tens digit decreases by 2 when we subtract 2 tens.

So the ones digit stays the same, that's still zero, but the tens digit changes because we're adding or subtracting a multiple of 10.

Andeep said, "I know that 2 less than 4 is 2." Izzy said, "So 2 tens less than 40 is 20." What do you notice? Can you see there are 4 ones and 4 tens? Andeep said, "I know that 4 subtract 2 is equal to 2.

So two less than 4 ones is 2 ones." "So 40 minus 20 is equal to 20." So if we subtract 2 tens from 4 tens, we are left with 2 tens.

So if 4 ones minus 2 ones is equal to 2 ones, then 40 minus 20 is equal to 20.

Let's check your understanding.

Are these statements true or false? 30 is 2 tens more than 20.

20 is 3 tens less than 50.

Pause the video while you think about whether these are true or false, and you could use cubes to help you.

Did you think these statements are true or false? So the first one is false.

30 is not 2 tens more than 20.

It's only 1 ten more than 20.

Andeep said, "3 is 1 more than 2 so 30 is 1 ten more than 20." What about the second statement? 20 is 3 tens less than 50.

That's true, Izzy said, "2 is 3 less than 5.

So 20 is 30 less than 50." Because 20 is 2 tens, so that's 3 tens less than 50, which is 5 tens.

Here's a task for you to have a go at.

Can you complete the equations with the missing multiples of 10? So here we've got 60 as the total and you're going to work out how many more groups of 10 do you need to make the total? And then, we've got 60 and we're going to subtract different multiples of 10 and see what you are left with.

So think about how many more groups of 10 do we need and how do you know? You could use cubes or straws to check, and don't forget, you can use known facts to help you as well.

Here's the second part of your task.

Can you pick two cards and see if they have the same answer? Keep the cards if they match.

So here we've got some multiples of 10 and we're going to either add or subtract a different multiple of 10.

See if you can work out what the answers are and see if you can match any that have the same answer.

You could play this game with a friend and see who can find the most matching cards.

Here's the third part of your task.

Can you play this game with a friend? Can you see we've got a number track with the multiples of 10 from 10 to a hundred? Throw a counter onto a number.

Write an addition or a subtraction equation with your multiple of 10 as the answer.

Remember to only use multiples of 10.

Colour in the number if you are right.

The first one to get a line of three wins.

So here's an example.

Andeep threw his counter onto the number 40 and he said, "I landed on 40.

My equation is 20 plus 20 is equal to 40." So can you see he's used multiples of 10 to make the total 40.

Izzy threw her counter onto the number 60.

She said, "I landed on 60.

My equation is 80 minus 20 is equal to 60." And she's used multiples of 10 to get the answer 60.

So they were both right so they can colour in their number and see if they can get a line of three.

So pause the video and have a go at your tasks.

How did you get on with your tasks? Did you complete the equations? So here we were finding numbers that will add to make 60.

60 is equal to 10 plus 50 or 20 plus 40 or 30 plus 30, 40 plus 20, 50 plus 10 or 60 plus 0.

And then, we had some subtractions here.

60 subtract 10 is equal to 50.

60 subtract 20 is equal to 40.

60 subtract 30 is equal to 30.

60 subtract 40 is equal to 20.

60 Subtract 50 is equal to 10.

and 60 subtract 60 is equal to 0.

Did you notice that the missing part was the same in each pair? So if you look at the addition and subtraction equations that are next to each other, we had the same missing part.

Did you spot that the difference decreased by one group of 10 each time? So we had 50 then 40, 30, 20, 10 and 0.

So we're going down by 10 each time.

I wonder why that happens.

How did you get on with the second part of your task? Did you find two cards with the same answer? You might have found 50 plus 20 which is equal to 70, and 80 minus 10 which is also equal to 70.

So those two match.

50 plus 30 is equal to 80 and so is 90 minus 10.

So those two match.

50 plus 40 is equal to 90 and so is 100 minus 10.

So those two match.

How did you know? Did you use a known fact to help you or did you use some cubes to help you? Izzy said, "I used known facts to help me." How did you get on with the third part of the task? Did you play this game with a friend? Andeep and Izzy played the game and you might have tried the same as them.

So Andeep said, "I landed on 40." Can you think of an equation that he might have written to make 40? So he's thought of 20 plus 20 is equal to 40.

Is that correct or not? Give it a thumbs up if you think it's correct.

Yes, that is correct, isn't it? How do you know? I know that 2 plus 2 is equal to 4.

So 2 tens plus 2 tens is equal to 4 tens.

So 20 plus 20 is equal to 40.

Well done, Andeep, you can colour that one in.

Izzy said, "I landed on 60." I wonder what equation she's thought of to make 60.

Izzy said 80 minus 20 is equal to 60.

Do you think that's correct or not? Give it a thumbs up if you think it's correct.

Yes, that is correct.

Well done, Izzy.

I know that 8 tens minus 2 tens is equal to 6 tens because 8 minus 2 is equal to 6.

Well done, Izzy, you can colour that one in.

Andeep said, "I landed on 50." Can you think of an equation that he might have written? He said 60 minus 10 is equal to 50.

Is that correct or not correct? That's correct, I know that's correct because 6 tens minus 1 ten is equal to 5 tens.

Well done, Andeep, you can colour that one in.

Izzy said, "I landed on 80." Can you think of an equation that she might have written that makes 80? She's written 60 plus 20 is equal to 80.

Is that correct or not correct? That's correct, isn't it? How do you know? Because 6 tens plus 2 tens is equal to 8 tens.

I know that because 6 plus 2 is equal to 8.

Well done, Izzy, you can colour that one in.

Andeep landed on 30.

Can you think of an equation that he might have written for 30? He's written 20 plus 10 is equal to 30.

Is that correct or not correct? That's correct, isn't it? I know that's correct because 2 plus 1 is equal to 3.

So 2 tens plus 1 ten is equal to 3 tens.

Andeep's got a line of three, hasn't he? Let's see if Izzy can get a line of three as well.

Izzy said, "I landed on 100." Can you think of an equation that would make 100? She said 60 plus 40 is equal to 100.

Is she correct or not? Yes, that's correct, isn't it? I know that 6 tens plus 4 tens is equal to 10 tens because 6 plus 4 is equal to 10.

Well done, how did you get on with yours? Let's move on to the second part of the lesson.

We'll be looking at missing number problems. We can use known facts to find missing numbers.

Can you see the part-part whole model here? And the equation has got a missing number.

We've got 80 plus 10 is equal to something.

Andeep said, "The whole is missing." Izzy is asking, "How can we work it out?" Can you think of a known fact that can help with this one? Andeep said, "I know that 8 plus 1 is equal to 9." "So 8 tens plus 1 ten is equal to 9 tens." Can we use that to help us work out the missing number? It's 90, so 80 plus 10 is equal to 90.

They all look similar.

Can you see they've all got an 8 or 1 and a 9 in them? So we can use our known fact to help us work out other facts.

We can use known facts to find missing numbers.

Here we've got another missing number.

We've got 80 is equal to 50 plus something.

This time, one of the parts is missing.

Izzy is asking, "How can we work it out?" Can you think of any known facts that can help you to work this one out? Andeep said, "I know that 5 plus 3 is equal to 8." "So 5 tens plus 3 tens is equal to 8 tens." Can we use that to help us work out the missing number? Andeep said, "So 50 plus 30 is equal to 80.

So the missing number is 30." They were all similar again.

Can you see that they've all got a 5, a 3, and an 8? So we can use 5 plus 3 is equal to 8 to help us work out other equations.

Let's check your understanding.

Which bar model will help to find the missing numbers? So we've got 4 tens plus 4 tens is equal to hmm tens.

40 plus 40 is equal to hmm.

So which bar model with these known facts will help us to work out the missing number? Pause the video while you think about this one.

So which bar model would you use to help you work out the missing number? Andeep said, "I know that 4 plus 4 is equal to 8." "So 4 tens plus 4 tens is equal to 8 tens." So the missing number is 8 tens.

So 40 plus 40 is equal to 80.

8 tens is equal to 80.

So the middle bar model helped us to work that one out.

Let's check your understanding again.

What are the missing numbers and how do you know? So here we've got 70 plus 20 is equal to something.

60 subtract something is equal to 20.

50 is equal to something, add 20.

And 70 minus 20 is equal to something.

So pause the video while you have a think about what the missing numbers are and how do you know? Can you use a known fact to help you? What do you think the missing numbers are? So the first one, 70 plus 20 is equal to 90.

Andeep said, "I know that 7 plus 2 is equal to 9 so 70 plus 20 is equal to 90." The second one, 60 minus 40 is equal to 20.

Izzy said, "I know that 6 minus 4 is equal to 2 so 60 minus 40 is equal to 20." The third one, 50 is equal to 30 at 20.

Andeep said, "I know that 3 plus 2 is equal to 5 so 30 plus 20 is equal to 50." And finally, 70 minus 20 is equal to 50.

Izzy said, "I know that 7 minus 2 is equal to 5 so 70 minus 20 is equal to 50." Is that what you thought? Here's a task for you to have a go at.

Can you fill in the missing numbers? Here we've got some bar models and part-part whole models with some missing numbers.

Sometimes the missing number is the whole and sometimes it's one of the parts.

You could use known facts to help you with these and you could check with cubes.

Here's the second part of your task.

Can you fill in the missing numbers? Think about how many more ones or how many more tens we need.

Can you use some known facts to help you with these? And you could check with cubes.

So pause the video and have a go at your tasks.

How did you get on with the first part of your task? So on the first bar model, the whole was missing and that's 6 because 4 plus 2 is equal to 6.

On the second bar model, we had one of the parts missing and it was 4 tens because 4 tens plus 2 tens is equal to 6 tens.

Then we had another missing part and that was 20 because 40 plus 20 is equal to 60.

We can use the known fact 4 plus 2 is equal to 6 to help us with the last two bar models.

Then on the part-part whole models, we had the missing whole that was 7 because 2 plus 5 is equal to 7.

Then we had a missing part that was 2 tens because 2 tens plus 5 tens is equal to 7 tens.

Finally, we had a missing part which was 50.

I know that 20 plus 50 is equal to 70.

I can use the first known fact to help me.

2 plus 5 is equal to 7.

So 2 tens plus 5 tens equal to 7 tens.

That's 20 plus 50 is equal to 70.

How did you get on with that one? Here's the second part of your task.

Did you fill in the missing numbers? So I can see that 9 is equal to 8 plus 1 and 7 plus 2 and 6 plus 3, 5 plus 4, 3 plus 6, and 9 is equal to 4 plus 5.

Can you see the pattern there? The total was always 9.

Then, we had 90 is equal to 80 plus 10, 70 plus 20, 30 plus 60, 40 plus 50, and 60 plus 30.

And finally, 90 is equal to 50 plus 40.

How did you know? Did you use known facts to help you with the equations with multiples of 10? Izzy said, "I used a known fact to help me.

I saw that as one addend increased, the other decreased." And I can see here that the additions that make 9 can help us to work out the additions that make 90.

We've got to the end of our lesson.

Today, we were adding and subtracting multiples of 10 and this is what we've learned: Unitizing and known facts can help you to add and subtract multiples of 10.

For example, if 3 plus 2 is equal to 5, then 3 tens plus 2 tens is equal to 5 tens which is equal to 50 and 30 plus 20 is equal to 50.

If 5 minus 2 is equal to 3, then 5 tens subtract 2 tens is equal to 3 tens which is equal to 30 and 50 minus 20 is equal to 30.

So we can use our known facts to help us work out additions and subtractions with multiples of 10.

Well done, see you next time, bye!.