# Lesson video

In progress...

Hi, everybody! Today, we are going to be using our number bond knowledge for numbers within 20 to do some adding and subtracting.

So let's get started for our lesson! Make sure you've got your math hats on, so put on your hat, tighten those ties, tell the computer: "Now I'm a mathematician!" Let's get started.

So here is today's lesson agenda.

First off, we're going to be looking at our star words.

Remember to make sure we need to use our actions whenever we use our star words-- so if you see me not using them, make sure you whisper at the screen: "Ms. Hill, you're not using your star word actions!" Then, we're going to be looking at number bonds, and using number lines to help us with our adding and subtracting.

We're then going to do some practise together before moving on to do our independent task.

So let's have a look at our star words.

Ooh--Before we even get on to our star words, these are things you will need for this lesson: pencil, some paper, and a ruler.

If you need to, pause this video and go get your resources before starting the lesson.

Brilliant, well done.

Here are our star words.

Remember, repeat after me: star words! Calculation strategy! So this means what strategy we are going to use to help us solve the equation.

We have partition; we have number bond; make ten; regroup; add, plus, subtract, minus.

Great job! Can you show me calculation strategy? How about partition? Number bond? And make ten? Great job.

Let's remember to use them together throughout this whole lesson.

Remember, I might need some reminding, too.

So here we have a calculation.

And my calculation is 36 add 47.

Now, we can use our number bonds within 10 to help us calculate this mentally.

But which number bond can we use? Well, have a look at your tens.

If I know that 3 add 4 is equal to 7, then I know that 30 add 40 is equal to 70.

So that's our tens we've added, and now we just have our ones.

And 6 add 7 is equal to 13.

Have I finished though? No, I haven't finished.

I need to remember to add 70 and 13 together.

And I know 70 add 13 is equal to 83.

Now, another really cool way of representing this equation or using a different calculation strategy: we can use a part whole model, or we can use this empty number line.

So the first number I'm going to put on my number line is 36.

Now, if I added 47 all in one go, it might get a little bit confusing.

So what I'm going to do is I'm going to partition the numbers and break them down into simpler numbers to add.

So I'm having a look at my ones.

I want to add 4, because if I add 4, I will get to 14, which will make adding a lot easier.

And then I will have 3 left over.

So first things first: I'm going to add 4, which will take me to 40.

I'm then going to add my leftover ones which is 3, which will take me to 43.

And now I need to add 4 groups of ten.

So I'm going to add my first ten, which will take me to 53; my second ten, which will take me to 63; my third ten, that will take me to 73; and my final ten, that will take me to 83.

Well done! It is equal to 83.

I have another equation here.

What I'd like to do is after I show you the equation, I want you to pause the video and see if you can use a calculation strategy which will help you to calculate this mentally.

Ready to pause the video? 3, 2, 1.

Pause the video! Super.

Well done.

Let's have a look at this equation together.

If I know that 8 subtract 4 is equal to 4, then I know that 80 subtract 40 is equal to 40.

Now for this one, I was a little bit cheeky.

I decided I'm going to keep the ones as they are, so 83 subtract 40 is going to be 43.

And 43 subtract 7 is equal to 36.

So you might have done yours a little bit differently, but we can still use our empty number line to help represent this equation.

So our greatest number is going to go first, because it is a subtraction equation.

And the greatest number is.

Brilliant.

It is 83.

Now we're going to do some jumping back.

So, 83 subtract 3 will get us to our nearest ten-- which is 30.

Excuse me, it's not 30 -- it's 80.

So 83 subtract 3 will take us to 80.

And then, we need to subtract some more.

We need to subtract 4.

So 80 subtract 4 is equal to 76.

We're going to jump back and do our tens now.

76 subtract 10 is equal to.

Brilliant! 66.

Subtract another ten.

56.

Subtract another ten.

46.

Let's subtract one more ten.

36.

Brilliant.

Great job.

Give yourself a big pat on the back! Now, it's your turn.

What you're going to do is going to use some different calculation strategies such as number bonds and using a number line to work out these six different equations.

We have 36 add 27 is equal to something.

65 subtract 17 is equal to something.

58 add 44 is equal to something.

54 subtract 26 is equal to something.

47 add 38 is equal to something.

And 83 subtract 46 is equal to.

Well, it's equal to something.

So remember, you can use different calculation strategies to help you solve these mentally.

Good luck, and remember to pause the video.

Great job, everybody.

Let's have a look at some more equations.

So, here we have 36 add 47 is equal to.

something.

Now, we're going to have to use our number bonds to 20, because we can see there's some regrouping here, 'cause 6 add 7 is over--going to be over 10, isn't it? So let's start off with our tens.

So, if I know that 3 add 4 is equal to 7, then I know that 30 add 40 is equal to 70.

So we've done our tens; let's have a look at those ones.

6.

6, 7, 8, 9, 10, 11, 12, 13.

6 add 7 is equal to 13.

Have I finished? No, I haven't finished! So now I need to add 70, add 13, is equal to.

83.

Now, it's going to be my turn.

Make sure you're carefully watching.

So here we have.

1, 2, 3, 4.

4 different equations.

And I'm going to be looking at the first equation, which is 72 subtract 34 is equal to.

Well, it's equal to something, isn't it? So now, it's my job.

Now, I'm going to use my number bonds first.

So, if I know that 7 subtract 3 is equal to 4, then I know that 70 subtract 30 is equal to 40.

And if I know that 42--take the gaff, I actually added that cheeky little one onto my 40s-- 42 subtract 4, well I need to count backwards.

42, 41, 40, 39, 38.

I'm also going to use a different calculation strategy and I'm going to draw a lovely, long number line.

So luckily, my number 32 -- it's 72, my number 72 -- is at the far end, and it's the greatest.

And I'm going to jump backwards.

So I'm using 72, subtract 2--because that was going to take me to my nearest multiple of ten.

So 72 subtract 2 is equal to 70.

Well done.

And I need to do some more jumping back.

72 subtract another 2--'cause remember, we're subtracting 34, so I've got 4 ones, and I've already subtracted 2-- so I'm going to subtract another 2, which will take me to 68.

And now we get to jump back in tens: 68 subtract 10 is equal to 58; 58 subtract 10 is equal to 48; 48 subtract 10 is equal to 38.

Therefore, the answer is 72 subtract, take away 34 -- is equal to 38.

You've got four different equations here.

You're going to use your different calculation strategies, such as number bonds within 20 and number lines, to solve them.

Partition these equations, and by using your number bonds to 20, solve them! Don't forget to draw your number line to double-check your answers.

Make sure you pause this video and complete the four equations in front of you.

Great job, everybody.

We're going to have a look now at the different answers to these four equations.

So 52 subtract 14.

If I know that 5 subtract 1 is equal to 4, then I know that 50 take away 10 is equal to 40.

And then I've got my leftover ones, so 42 subtract 4 is equal to 38.

12 add 49: well, if I know that 1 add 4 is equal to 5, then I know that 10 add 40 is equal to 50.

And if I know that 2 add 9 is equal to 11, then I need to add these two separate numbers together and 50 add 11 is equal to 61.

My third equation: I have 84 subtract 45.

If I know that 8 take away 4 is equal to 4, then I know that 80 subtract 40 is equal to 40.

And if I know--well, having a look at-- I can't really do 4 subtract 5.

So, I need to do 44 subtract 5, and this is equal to 39.

For my final equation: 24 add 59.

If I know that 2 add 5 is equal to 7, then I know that 20 add 50 is equal to 70.

And if I know that 4 add 9 is equal to 13, then I know that 70 add 13 is equal to 83.

Great job, everyone! Make sure you tick and fix and tell yourself, "1,2,3, well done, me!" Brilliant job, everybody.