Lesson video

Hi, my name is Ms. Jones, and I'm going to be taking your maths lesson today.

And I am super, super excited to get started.

Actually maths is my favourite subject.

Do you want to know why? It's because math is all about solving problems. So if I really try hard in maths and I learned to be a problem solver.

I can solve any problems wherever I go, which might come up in my daily life.

Anyway, shall we have a look at what we're doing today so we can get started? Okay.

So today we're going to be looking at some problems and understanding which operations in those problems have equal priority.

Hmm equal priority.

You probably might be wondering what that might mean.

But don't worry.

Today we will explain all.

Okay.

On our agenda today, we're going to be starting with some addition and subtraction problems, then multiplication and division problems. And then we've got our task and our quiz.

You will need a pencil and a piece of paper for this lesson.

So if you haven't got one, please go get one now.

Pause the video and press play when you've got them.

Okay, let's start by looking at this problem.

Now in this problem, we've got Laura in our math story with 30 sweets.

Now we've got some items that happen.

For example, she was given 15 more then she gave 10 away.

And what we want to explore is whether it matters.

If we change the orders of these items or these operations around, I want you to have a think about that.

Does it matter if I move these green items around will I still get the same answer? Pause the video now and have a think about that.

Okay.

Let's move on.

What I've done is I've tried it one way.

So when trying it with this order, see what answer we get.

So she started, we know with 30 sweets.

Now, first of all, I've got Laura ate 12 of her sweets, which brings us down to 18.

Laura then gave 10 away to her sister, brings us down to eight.

Then she added 15.

She was given 15 more, 23.

And finally she dropped six of her sweets, which brings us down to 17 sweets.

Laura ends up with 17 sweets.

Okay.

So what happens if I change some of these around, will I still get the same answer? Let's try it.

So this time I've switched some of the green items around and again I'm starting with 30, but I'm going to start this time with adding 15, I get 45.

Then I'm going to take away 10 Laura gives 10 to her sister, 35.

Then Laura ate 12 of her sweets, lucky her, which brings us down to 23.

And then Laura dropped six of her sweets.

Laura ends up with 17 Sweets That's interesting.

We got the same answer as before.

So I'm thinking maybe it doesn't matter which order we do the operations in.

And we've got here both addition and subtraction.

Hmm, let's investigate this a little bit further.

We've got our Let's Explore task.

Now what I'd like you to do here is have a look at three different ways of using operations starting with 29.

So what you need to do is think about, does it matter in each of these? If I change the order of the pink and green cards, will I still end up with the same answer? If you want to, you can use a number line like I did.

Use your number line and track what's going on each time.

See if you end up at the same answer.

Okay.

Pause the video now and have a go at that.

Okay.

Let's just take one of those problems and explore it a little bit.

Here we've got two pupils who are offering their ideas.

So let's take this girl and she says, because subtraction is the inverse of addition.

If we add first and then subtract, it's like, we aren't doing the adding.

If we subtract first, then add it's like we aren't doing the subtraction.

So she's pointing out that addition and subtraction are the inverse of each other.

So it doesn't matter.

She says, if we do them in different order, because it's like undoing what we've done.

This boy here says that it doesn't matter which order we put the cards in.

The answer is still the same.

Now, when I had to go at this one, I did it in this order and I got 41.

I'm going to try in a different order and see if I still get the same answer this time I might add 17,29 add 17.

Same as 30 add 16 is 46.

Then I take away 10, I get 36.

And then I'm going to add five, 36 add five is also equal to 41.

Interesting.

So I think what we found out is that with addition and subtraction, we can change the order and we still get the same answer.

Lets summarise that on the next page, addition and subtraction have equal priority.

That means they're just as important as each other and we can switch them around and it doesn't affect the answer.

Now, if we're thinking about multiplication and division, I wonder if that's true for those as well, because they are the inverse of each other.

So perhaps we can switch those around let's investigate and look at a multiplication and division problem.

Here we've got again, a problem with a few things happening.

So let's read the problems see if we can find out what's going on, Amir, Ben and Freddie are washing cars to make some money.

Good for them I say, okay, for each car, they wash, they get 12 pounds to share.

They wash four cars per hour and they work for eight hours.

Okay So we know here that they getting 12 pound for each car, and then they wash four cars every hour so we're multiplying by four and they work for eight hours.

So we're multiplying by eight.

Of course they may have to share their money.

There's one, two, three of them.

So after those bits of multiplication, we also need to divide by three.

Have a look at the three calculations and think about which one will help us find the correct answer for the total amount of money they earn each.

Pause the video now and have a think about that.

Press play when you're back.

Okay.

So we've got all three calculations here and they're all multiplication division.

So all inverse operations of each other.

Let's see what answers we get.

So if we did 12 times four, we get 48 and then we need to multiply by eight, we get 384.

And then we divide by three, which gets us 128.

Okay.

So get the second one.

So first of all, we're dividing 12 by three, which gets us to four.

Then we multiply by eight, which gets us to 32.

And then we times by four, and again, we get 128.

These answers are the same, even though we've done it in a different order.

Let's just check that third one.

So four times 12 is 48 and then we divide by three to get 16.

And you can get what we're going to You can guess what we're going to get.

16 times eight is 128.

We've done this in three different orders because we've only used multiplication and division.

It's okay.

If we change the order, we still get the same answer.

So what have we found out here? Multiplication and division also have equal priority.

They're just as important at each other.

And if we switched them around, it's not going to affect our answer.

Okay.

Let's have a look at your main task today.

So using what we know, we know that addition and subtraction can be changed in any order.

Multiplication and division can be changed in any order.

So what I'd like you to do is solve the following calculations.

I'd like you to decide which order you're going to do the operations in in order to complete them in the most efficient way.

So for example, you might not want to start with taking away 36 because that might be more difficult to do for you.

You might start by adding 21.

You can choose the order.

So choose the order you think is most efficient and then solve each of these calculations.

I would like you to pause the video and go and have a go at that main task.

When you've finished your task, come back to the video and we'll go through the answers together.

Welcome back as promised, we are going to look at the answers to each calculation.

Now you might not have done it in the order that's on the slide because you might've changed the order, which is absolutely fine.

So we're just going to go through the answers, to check that you worked out the calculations correctly.

So number one, we should have got 118, number two 62, number three 70 number four 126, number five 96 and number six, 400.

How did you do? Hopefully that going through this lesson helped you to realise you can change the order and that hopefully helped you work these out accurately and efficiently.

Just before we finish though, I've got a final question for you to think about.

We know that additions, addition and subtraction can be switched around.

We know that multiplication division can be switched around.

What if we mix those together? This problem has addition and multiplication.

Before you go, I'd like you to think about these two operations.

Does it matter if we change the order around here? Pause the video now and have a think.

Let's have a look.

Shall we? Okay.

So if we add three to four, we get seven.

Then if we multiply by three, we get 21.

Now, if I change these around and I do four and then I multiply by three, I get 12.

If I then add three, I end up with 15.

We've ended up with two different answers.

How interesting.

And this is something that maybe we can go on and explore further after the lesson.

I think now it's time for you to complete your quiz all about equal priority operations.

I hope you enjoyed today's lesson.

That's it for me.

And see you soon.