Lesson video

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Welcome to your math lesson with me, Mrs. Harris.

We're going to be looking at applying addition and subtraction skills.

We're going to have a really quick look at language.

Then we'll move on to efficient addition, followed by addition and subtraction with decimals, and we'll finish with your independent task.

You're going to need a few things, a pencil, maybe a rubber, a ruler, paper to write on, or maybe a book.

If you don't have these things, pause the video, and go and find them now.

That's everything you need? Let's start with the language.

What words in a word problem, show whether it's an addition or a subtraction question? Just quickly let some pop into your mind.

Here's some, I found, some quite common ones, add, subtract, minus, plus, difference, greater than, less than, sum, but what's the word in this problem that tells us if it's an addition or a subtraction problem? What is the weight on earth of a average human elephant and rhino all together? That's right.

It was the word all together.

Wasn't it? So we can solve this problem, by adding their weights all together.

So, first of all, we need to look at the chart, at the table, to find their weights.

Got them? And then we need to add them together.

We're going to do that by using some known facts, seven plus three equals 10, so 7,000 plus 3,000 equals 10,0000, 200 plus 72 is 272.

Therefore their weight altogether is 10,272 newtons.

Another problem, addition or subtraction? How much more does an elephant weigh on Jupiter than it does Venus? Well is the how much more that gives us a clue what we need to do.

We need to find the difference.

So I'm going to go with subtraction this time.

I found the data I need on my table, and I'm going to show it as a number line.

The first thing I wanted to do though, was round 6,480 to 6,500.

Can you see why I did that? It's only 20 away from that number, and it gives me a much more friendly number to subtract.

So I started with my min end 18,720, I've taken away 6,500, to get me to 12,220, but I need to remember to add back on that 20.

And so the answer is 12,240 newtons.

Let's have a look at efficient addition.

So, what's the total weight of all the animals listed? We know it's going to be addition, 'cause we need to find the total, the sum.

So I'd like you to show two different ways of solving this word problem.

Pause the video and have a go now.

Well done for having a go at this problem.

We had a lot of add-ins to add together.

So what I did first was I added what I could in my head to reduce the number of add-ins, and then I did column addition.

Did you find two ways of solving it? And did you arrive at the same answer as me? 27,726.

There was one of us gone wrong a little bit along the way.

Let's have a look together.

That's addition and subtraction with decimals.

Money is a great real life way of dealing with decimals, and something we probably all do in everyday life.

This problem is about somebody called Lily, and Lily buys two models.

The total cost is £13.

48, and she pays with a £20 note.

How much change does she get? So, this is a subtraction problem because we need to find out the difference, but we know that subtraction is the inverse of addition, so we could work either way.

I'd like you to have a think.

What would you prefer to do? How do you know and what strategy might you use to solve this problem? Not asking you to solve it yourself.

Hey, had a think? Let me show you how I solved it.

So we already talked that we could go both ways, we could do addition or subtraction.

So first, I decided to do addition.

I added £0.

52 to my £13.

48 to make it £14.

And then I easily knew that from 14 to 20 is £6.

On the other hand, I decided to do some subtraction, around it my 13.

48, up to £14, and then, because the difference was £0.

52, I added that back on.

Either way, I got the same answer, she got £6.

52 in change.

Let's try another problem.

A model replica of a space shuttle costs 13.

75, the model replica of the International Space Station, was £29.

65 more than the space shuttle model.

Cos buys both models.

How much does he spend? Well, is this an addition or subtraction question? How do you know, and what strategy might you use, to solve this problem? Once again, pause the video and have a think.

I'm still not asking you to solve it, just how you would go about it.

That's an idea.

So this is what we're going to do.

We need to do some addition.

Don't we? We want to know how much he spent.

We've got more than one step here.

We know how much the space shuttle costs.

And we know that the International Space Station, costs £29.

65 more than that.

So we'll put both figures in to our power model.

Now we need to find the total.

How much did the International Space Station cost? We're going to add 13.

75 to 29.

65, and then we get our answer.

So Cos did this as well.

So he first did it with column addition, 13.

75 plus 29.


And Cos found out that his space station cost 43.


He would have done it on a number line, and he did that to check.

Is 43.

40 the total amount cost spent? No, it's not.

That's the cost of the International Space Station.

So now we need to find out, how much he spent.

Now I do need to do some addition.

Have you found how much he spent? Well, if we had these figures, the total cost of the International Space Station, and the space shuttle, we can then add them both together, to find out that his total spend, and is this what you got, was £57.


Now it's time for you to do your independent learning.

So pause the video to complete your task.

Welcome back.

How did you get on with the independent learning? There was some quite meaty problems, weren't they? I hope you found a strategy that worked for you, and these are your answers.

So the question one, we have 12,240 newtons.

You should have the digits one, two, two, four, zero.

Question two's answer was 8,741 newtons.

Eight, seven, four, one.

And your last question, question three.

The answer was 10,290 newtons.

So the digits you should have written down were one, zero, two, nine, zero.

Well done everyone.

Now, just before I go, it's time for me to say, if you'd like to share any of your work with me, or everybody at Oak National, ask your parent or carer to do it on Twitter or other social media, tagging @OakNational.

Now just to show me everything you've learned, pop along to the little multiple choice quiz.