Lesson video

Hi everybody, Miss Hill here.

Today, we are going to be doing a little addition and subtraction using round and adjust.

So let's get ready for our lesson.

Put on your hats.

Tighten those ties.

Tell the computer, "Now I'm a mathematician." Let's get started.

Here is today's lesson agenda.

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

Then we're going to be exploring for round and adjust.

Then we're getting into practise before moving on to our independent task.

So before we get started, please make sure you have the following resources in front of you.

A pencil, a piece of paper, and a ruler.

If you need to, pause this video to go collect all of those bits before we get started.

Here are our star words.

Remember, you need to repeat them back to me.

Star words.

Near multiple.

Remember, we're jumping on our number line.

So we have our near multiple.

Round.

Adjust.

Strategy.

Efficient.

Repeat them back to me.

Near multiple.

Show me round.

Show me adjust.

Show me strategy.

Show me efficient.

Nice job.

Remember, we need to be using our star words throughout our lesson to help us remember our key vocabulary for this lesson.

If you spot that I haven't used it in action, remember to say, "Miss Hill.

You haven't used your star words properly," and hopefully, I'll be able to hear you through the screen.

Let's get started.

So I want to calculate the total of this addition.

44 add 49.

Now, I could use this.

44 add 50.

How could I use this? Well, let's have a look.

Here I've got a part whole model with my deans.

Now, 'cause I have these deans, I'm going to try and count them all.

Now, can you help me? 10, 20, 30, 40.

Ooh, I'm going to come back to these ones in a minute.

50, 60, 70, 80.

Now I need to add the ones.

81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93.

Whew, deary me.

That's not the most efficient way of adding, is it? So how could the calculation 44 add 50 make it more efficient for me to use this equation? Well, I can see that 50 is actually one more than 49, and I can use my number ones to help me solve this, as long as I remember I've added that cheeky extra one.

If I know that four add five is equal to nine, then I know that 40 add 50 is equal to 90, and I've got that four.

91, 92, 93, 94.

Now I need to remember to subtract one, because I actually added it when I didn't have it.

The answer is 93.

How much more efficient and quicker was that? Let's have a look at another equation together.

So I want to calculate the total of this equation.

44 add 51.

How could this calculation help me find the answer? I wonder.

So here I have my deans again.

Let's do some counting.

10, 20, 30, 40, 50, 60, 70, 80, 90, 91, 92, 93, 94, 95.

Now, is that the most efficient way of counting? I don't think so.

But if I use my number facts, and I know that 50 is actually one less than 51, I can do the same again.

So if I know that four add five is equal to nine, then I know that 40 add 50 is equal to 90, and four add zero is four, so 94.

But then remember, I need to add that extra one, so it becomes 95.

Brilliant.

So here I've got two additions.

We've just done them together.

44 add 51, and 44 add 49.

So we can use our round and adjust.

So round and adjust, which is when we did our one more and adds, or we can do our partitioning.

Which do you prefer? Why? Hello everyone.

My name is Miss Jones, and I'm going to tell you which one I prefer.

I prefer the round and adjust strategy.

Do you want to know why? Because I find it for calculations like the ones we've just looked at, more efficient, because I can still work the answer out accurately, but I can also solve it a little bit more quickly than other strategies.

Let me show you how I might work one out, representing and using a representation called a number line.

I'm going to look at this one.

I've got 39 plus 46.

Now I know that 39 is close to 40, so this might be a good equation for me to use my round and adjust strategy.

Now, I could represent it like this, and use a partitioning strategy, but it might take a long time.

10, 20, 30, 40, 50, 60, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85.

I'm getting out of breath trying to do that, and if I try it here regrouping my ones, it might take even longer.

So I'm going to use my round and adjust.

I'm going to show it on a number line.

Now I'm going to start with 46, and then add on 40 and adjust.

Now, I can start with 46, as I know addition is commutative.

I can start it with any one of these, add on the other, and I'll still get the same answer.

So I'm going to add on my four tens, 40.

Now you can do that in groups of 10, or jumps of 10 like this, or you might be able to do one jump of 40.

46 add 40 is equal to 86.

Now look at my original number sentence at the top.

I didn't have 40.

I had 39.

So what do I need to do to 86? I need to adjust.

So I'm going to take away one, subtract one, and I end up with 85.

39 add 46 is equal to 85.

Okay, I'm going to pass you back over to Miss Hill, who's going to talk through what you're going to do next.

Now in fact, it's actually going to be your turn.

So you are going to be doing these four equations.

33 add 49, 28 add 65, 25 add 38 and 19 add 34, and you are going to use round and adjust.

You need to make sure that you draw your number line, and remember if you're adding to get to your nearest multiple, be very careful.

Don't forget to adjust.

Good luck.

Pause this video, and see you soon.

Great job everybody.

So now we've done some additions, and now we're going to do some subtractions.

So here I have 54 subtract 29, is equal to.

Something, and this is what we're going to work out now.

Here I have my beautifully straight number line drawn with a ruler, and I have the number 54.

Now 54 subtract 29.

I need to break that up into manageable steps, so it's easier for me, and will be the most efficient way of doing this strategy.

So 54 subtract 4.

Now, I've subtracted 4 because that will take me to my nearest multiple of 10.

I'm supposed to subtract nine.

I've only subtracted four.

So at the end, I must subtract that extra five.

So I'm going to keep that five in my hat.

So here we go.

54 subtract four is equal to 50, and now I get to take away some 10s.

50 take away 10 is equal to.

Well done, it is 40.

40 take away 10 is equal to.

I can't quite hear you.

Brilliant.

It is 30, and what else do I need to make sure I'm subtracting? That five, and 30 subtract five is equal to 25.

Well done.

What an efficient way of doing it.

So I'm going to show you what you are going to be doing for your independent task, and here we have four equations.

I'm going to pick.

I'm going to pick 44 add 29 is equal to.

Now, I'm going to draw my lovely number line, and the first number I'm going to put on my number line is 44.

Now first things first, I know I want to round to my nearest multiple of 10 to make my life much easier.

So my nearest multiple of 10 is 50, so I'm adding six.

I'm adding six.

Now I know I actually need to add nine, so six.

The difference between six and nine is three.

So at the end, I need to make sure I add an extra three.

So I'm going to put that three in my hand and put it in my hat.

So 44 add six is equal to 50.

Now I get to add my 10s, which is my favourite bit.

50 add 10 is equal to 60.

60 add 10 is equal to 70, and don't forget, I need to add that cheeky little three on the end, which is equal to 73.

So 44 add 29 is equal to 73.

How efficient is that? So it's your turn now, and you have four different equations.

24 add 59 is equal to something.

82.

You guys, you just reminded me.

Thank you so much.

I need to use my star words actually.

Let's try again.

24 add 59 is equal to something.

82 subtract 39 is equals to something.

29 add 24 is equal to something, and 74 subtract 38 is equal to something.

Now please remember to draw your number lines, and my top, top tip.

Remember to adjust.

Remember to put those extra numbers into your hat, in your lap for the end.

Now remember to draw that number line with a beautiful ruler, a lovely, sharp pencil, and make sure it's the neatest work you have done all day.

I can't wait to see what you come up with.

So let's pause the video, and I'll see you on the other side.

Great job, everybody.

Now give yourselves a little pat on the back, 'cause that was a lot of work.

So let's have a look.

Excuse me, at the first equation together.

So 24 add 59 is equals to 83, and here you can see I've jumped up to 30 by adding my six.

Remember, I need to add an extra three, added my 10s, and added my three at the end.

So the answer is 24 add 59 is equals to 83.

My next equation for 82 subtract 39.

Now you can see, my numbers are going the other way, 'cause I'm actually going backwards.

So 82 to my nearest multiple is 80.

I need to subtract two, and I have to remember, I have to subtract an extra seven at the end.

You can see I've subtracted my two, and then my lovely 10s, which is my favourite bit, and subtracted that seven.

So 82 subtract 39 is equal to 43.

My next sum.

29 add 24 is equal to.

It's 53.

So you can see.

I've rounded to my nearest 10, which I only added one.

So I have to remember to add that extra three.

I've done my two jumps of 10, and landed 50.

I added my three to get 53, and finally last but not least.

74 subtract 38 is equals to.

Well, it's equal to 36.

You can see I've rounded to my nearest multiple of 10.

So I've subtracted four.

I've done my three jumps of 10 back, and subtracted another four.

Well done everybody.

Remember to tell yourself, "One, two, three, well done me." And if you're lucky enough to be working with somebody else, tell them, "One, two, well done you." Brilliant.

Great job everybody.

You have done a super job today using round and adjust.

If you'd like to, please ask your parent or carer to share your work on Instagram, Facebook or Twitter, tagging @OakNational and #LearnWithOak.

I've had a super lesson with you today.

Can't wait to do some more learning with you again another time.

Take care, and have a great rest of your day.

Bye.