Lesson video

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Hello, welcome back to our unit on exploring calculation strategies, today's session we're going to be solving subtraction equations.

for this lesson, you will need a pencil and some paper.

Please pause the video now to go get these things.

If you haven't gotten them already.

Okay then, well, I thought we'd start off today's session with a little riddle.

So what's orange and sounds like a parrot.

Have a think.

Well done to those of you that got it right.

It is in fact a carrot.

Right let's get ourselves started with today's session there.

So as I said, at the beginning of the session, we are going to be learning how to solve subtraction equations.

We're going to start off with a quiz to test your knowledge.

Then we're going to look at today's star words, going to be looking at different strategies you can use to solve subtraction equations.

Then there'll be a talk task then you'll have chance to answer.

Sorry.

We will have chance to answer some subtraction equations together.

Before you have chance to have a go at your independent tasks, we'll review the answers together, and then there'll be a final place to see what you've remembered.

Welcome back, right now let's cut start off today by looking at today's star words.

So we're going to use my turn, your turn.

I'll repeat, I'll say the words.

I mean, you repeat back to me, so start with make ten, number bonds, partition known facts round and adjust equation Okay, then so we're going to start the session by looking at our new learning.

We've got an example here we've got 56 subtract 30.

What I want you to do is think about how we can solve this equation and what subtraction strategies we already know.

I don't at this moment want you to have a go at solving the equation.

I just want you to think about these two questions.

Okay.

What we already know is we know we have to solve it.

We can solve it by using a range of different strategies.

So let's have a look at the strategies we could use today to solve this equation.

So we could use known facts so if I know that 5 subtract 3 equals two, then I know that 50 subtract 30 is going to equal 20.

I could also use a different strategy today.

I look at those two numbers.

I can see the 30 is a multiple of 10, so I could use a strategy called counting back in my tens by starting at 56 and counting back in my tens three times.

So those are the two main strategies I could use for this example.

Now I've chosen today to count back in my tens.

I have a thing.

Why do you think I've chosen that strategy? I've chosen that strategy because I think it's the most straightforward when I've got a multiple of 10.

So want you to join in with me.

We're going to put 56 in our head and we're going to count back in our tens three times 56, 46, 36, 26.

We think our answer is 26.

Let's double check because I've done it with some deans.

Just to double check our answer.

So, and here we have 56 one, two, three, four, five tens and one, two, three, four, five, six ones.

I want to take away 30.

We've got one, two, three tens.

Yeah and it's left me with two times 20 and one, two, three, four, five, six ones, twenty six.

So we were absolutely right and I like that.

we're going to look at another example now in calculating 75, subtract 29.

I want you to have a thing this time about the strategies that we could use.

I'm going to give you five seconds thinking time to think about different strategies we could use to solve this equation.

Okay then.

let's have a look at those strategies, So we could partition the second number 29 into boating and nine, we could then do 75 subtract 20, which would give us 55.

Then we could do 55, subtract the nine, which would give us 46 that's one method.

Or we could do round and adjust.

Because when I look at this, I know that 29 is close to 30, which is a multiple of 10.

And I know I can count back in my tens really well.

It's one less.

So if I did 75 subtract 30, it would get me to 45 that I have to add back on one would just it, because I've taken away one too many strategy that I would use would be rounded, adjust and count back in my tens because I think that's the most straightforward strategy to use here.

When I've got a number that's so close to a multiple of 10, right? Then it's time to do today's talk task.

You're talking to us today you've got two equations.

You've got 97 subtract 40, and you've got 76 subtract 19.

I want you to have a think about which strategy you would use.

Remember, you can use the, say it out loud.

I will use strategy to subtract.

I can partition into, and I have chosen this strategy because.

My challenge to you today is, can you explain why you would use that chosen strategy? Pause the video now to have a go at today's talk to ask.

Welcome back, but then let's have a look at developed learning.

Lets have a look at our equation 28, add something equals 64.

It looks a little bit different to the equations that we've just been looking at.

How does it look different to you? I've noticed that I've got a box with a missing number.

I don't know that number.

So to solve this equation, I've decided to use my part whole model because this time I've been given my whole, I know it's 64.

And I think if I'm one of my part, I know it's 28, but I don't know my unknown is what that missing number is here.

How can I find that out? Well, done to those of you who said you need to do 64, subtract 28 to find out what this missing number is here.

Some will think about the best strategy for that.

So I've got 64 and I want to take away 28.

As soon as I look at this equation, I know that 28 is close to 30.

So I've chosen today to use my round and adjust strategy and count back in my tens three times, once I've done that, I have to adjust it.

So like you to join him with me, we're going to put 64 in our heads.

And we're going to count back in our chests three times, three times we'll then work out how we adjust afterwards.

So 64 and our heads counting back and our towns, 54, 44, 34, I've taken away three tens.

I've taken away 30 to give me 34, but I've taken away to too many.

So I need to add those two back on my answer to give me the correct answer, which would be 36, because 34 up to is 36.

Let's check it with our deans.

I have one, two, three, four, five, six tens here.

So 60 and one, two, three, four ones, 64.

I have two tens here.

One, two, and I have one, two, three, four, five, six, seven, eight.

Oh, I've accidentally got one too many here.

So I need to imagine that I've crossed that out.

I should have 28 here.

I've taken them away.

I then need to have six here, if it's correct.

One, two, three, four, five, six.

Absolutely and I should have three tens here one, two, three tens, so my answer is 36.

We've just accidentally put one too many ones in our ones column here.

You have got four different equations.

You've got questions on this side and you've got another slide with equations afterwards.

What I would like you to do today is have I got solving equations and then explain how you solve them.

Okay, welcome back.

Let's have a go there and going through our answers.

So our first equation ,was 83 subtract 29.

As soon as I looked at this, I knew I needed to use rounds and adjust to make 29 into 30 by adding on one, I then counted down three tens to get back down to 53.

Then I have to add on one because I'd taken away one too many.

Question two.

87 subtract 9.

And I had my missing number here this time.

Again, when I looked at this, I knew straight away I needed to use round and adjust to take away pen instead of nine, because I knew nine was very close to 10 that gave me 77 and then had to add one on because I'd taken away one too many to give me 78.

Question three.

98 subtract 50.

This time I solved my equation by counting back in my tens from 98, five times to give me 48.

And last but not least.

Question four.

76, subtract 38.

I use this equation by using round and adjust to make 38 into 40 by adding two on.

Then all I did was count back in my tens four.

Sorry, got a bit carried away that I counted back in my tens four times to get to 36, but I had to then add two back on because I'd taken two too many away, which gave me 38, well done for working really, really hard today too I've been very impressed.

Pause the video now to have a garden final quiz and answer a few questions based on what we've been learning today.

See you again soon.

Thank you for joining me.

Bye.