Lesson video

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Hello, welcome to your maths lesson with me, Miss Jones.

Let's have a look at what we're going to be doing today.

In today's lesson, we're going to be subtracting fractions.

We're going to start off by looking at some fraction problems, involving subtraction and representing them with bar models.

Then we've got some more abstract calculations for you to solve in your independent task and then finally, a quiz.

You'll need today something to write with and something to write on, such as a pencil and piece of paper.

If you've got a ruler, it might be helpful as we're going to be drawing bar models but don't worry if you don't.

If you need to pause the video and get what you need, please do so now.

If you've got everything, let's begin.

A quick starter.

I want you to tell me what the missing number or missing fraction is.

Whilst you're doing so, I want you to presume that all of these are equivalent to one whole.

Pause the video now to have a go.

Okay, let's have a look together.

So we know that our bar represents one whole.

If we're working in eighths, one whole is equivalent to 8/8.

Already we have 1/8 and 5/8 as our parts.

So that's 6/8 all together.

So our missing part here is going to be 2/8.

I know that one plus five plus two is equal to eight.

So 1/8 plus 5/8 plus 2/8 is equal to 8/8 or one whole.

So here, we have 2/5 and 1/5.

So we have 3/5 all together.

So this missing part must be 2/5.

And finally, we already have 4/9 and 3/9, which is 7/9.

So our missing part is 2/9.

Okay, let's have a look at this problem together.

Amrita has 7/8 of a kilometre to walk to school.

If she has walked 2/8 of a kilometre, what fraction does she have left to walk? How could we represent this using a bar model? Now, a bar model is a really helpful way to help us make sense of a problem be we end up solving it.

So when we're drawing our bar model, we need to think about what do we know already and what's unknown? What do we want to find out? So here, we know that we're working with a kilometre but her journey to school is 7/8 of a kilometre.

We also know that she's already walked 2/8 of the kilometre.

So here's my bar model.

Now, these eight bars represent a whole kilometre.

We know that her journey to school though is only representing this section, which represents 7/8 of a kilometre.

We know she's walked 2/8 already and this is what we want to find out.

How much she's got left to walk.

Now, we can actually clearly see, using our bar model how many parts are left.

One, two, three, four, five parts.

Now, what are our parts called? We're working in eighths.

So she has 5/8 left to walk.

Now, if we were representing this as an equation, we could think about this as a subtraction equation.

Our whole was 7/8.

We're taking away one part, the bit she's walked already.

2/8 and that's equal to 5/8.

Now, look at our numerator and our denominator here.

Our numerators have been subtracted.

Seven parts take away two parts or 7/8 take away 2/8 is equal to 5/8.

Our denominators have stayed the same because we're working in eighths of a kilometre throughout the problem.

Now, what we're doing here is applying known facts to subtracting fractions.

I know that seven take away two is equal to five.

Therefore, I know that 7/10 subtract 2/10 is equal to 5/10.

I know that 7/100 subtracting 2/100 is equal to 5/100.

And the same logic can be applied when subtracting fractions.

7/8 subtracting 2/8 is equal to 5/8 or we could say that 7/9 subtract 2/9 is equal to 5/9.

Let's look at another problem.

George slices an apple into 12 equal slices.

He eats five slices and gives the rest to his sister.

What fraction of the apple did his sister eat? How could we represent this using a bar model? I'd like you to pause the video, have a go at representing this as a bar model and then solving it.

Okay, let's have a look together.

So when representing as a bar model, we need to think about what we know already.

Well, we know the apple was divided into 12 equal slices or 12ths.

Here, we can say that this area is equivalent to one whole or 12/12.

We know that he's eaten five slices and he's given the rest to his sister.

So we can say that this is 5/12 if I'm working with one whole apple here.

And the rest, we're not sure of.

He gives this to his sister.

But we can say that we've got here one whole or 12/12, subtract 5/12 is equivalent to our unknown.

But how can we write this as an equation? Have a quick go now.

Okay, hopefully, the bar model helped you think about how we might write this as an equation.

We know that our whole was 12/12 and we were subtracting one part, which was 5/12, the amount that he's eaten.

And we need to find out the other part, which is 7/12.

Our numerators ge subtracted, so 12 take away 5 is equal to 7.

And our denominators stay the same.

We're still dealing with 12ths of that apple.

Okay, it's time for your talk task.

I'd like you to look at each of these subtraction equations and work out what the answer might be.

You can use the sentence stems below to help you make sense of the problems and convince me that you're right.

Pause the video now to have a go.

And then when you're done, come back and press play and we'll go over the answers together.

Okay, let's go over these.

So a, 7/8 subtract 3/8 is equal to 4/8.

I know that seven subtract three is equal to four, so therefore, 7/8 take away 3/8 is equal to 4/8.

Our numerator's four and my denominator is eight.

Let's quickly go over the others.

B, 5/6 subtract 3/6 is equal to 2/6.

C, 8/9 take away or subtract 2/9 is equal to 6/9.

And finally d, one whole, which we know is equivalent to 7/7 if we're using sevenths, subtract 2/7 is equal to 5/7.

When looking at these, what did you notice about some of the answers? Well, we could use our knowledge of equivalents to write these in a simpler form.

I know that 2/6 is equivalent to 1/3.

I know that because the same thing has happened to the numerator as our denominator.

We can divide our numerator by two and our denominator by two.

1/3 is a simpler version of writing 2/6.

Now, can you think of an equivalent for 6/9? Well, we know both of these can be divided by three.

So let's do that.

6/9 is equivalent to 2/3.

Both of those answers are correct but 2/3 is a simpler way of writing 6/9.

Now, in your task today, as a challenge, I'd like you to think about creating your own maths problem or maths story for some of the equations.

Here, we have an equation, 7/8 take away 3/8 is equal to? Well, I could work out the answer to this.

7/8 take away 3/8, I know that seven take away three is equal to four.

So my denominator stays the same.

I'm dealing with eighths.

My answer is 4/8.

I know that also I can divide both my numerator and denominator by four and I know that 4/8 is equivalent to 1/2.

But as a challenge, can I come up with a maths story? Pause the video now to see if you can came up with your own maths story, a worded problem that you could use for this equation.

Okay, now, yours is definitely going to be different to mine but here's my one.

There is 7/8 of a tin of paint.

Lilli uses 3/8.

What fraction of the tin is left? So for a subtraction problem, often the idea of starting out with an amount or a fraction of an amount using some of it and thinking about how many is left is quite a nice idea to start with.

Okay, it's time for your task.

I'd like you to find the answers for each of these.

As a challenge, can you create a maths story for each calculation? And also, you might want to think about can you find an equivalent fraction, which is simpler than the answer that you've got? Okay, pause the video now to complete your task.

When you've finished, come back to the video to see the answers.

Okay, let's go through these together.

So we had 4/6 subtract 2/6 is equal to 2/6.

Now, you might have also put that that is equivalent to 1/3.

6/8 subtract 5/8 is equivalent to or equal to 1/8.

2/3 subtract 1/3 is equal to 1/3.

3/4 take away 1/4 is equal to 2/4, which is also equal to 1/2.

6/7 take away or subtract 4/7 is equal to 2/7.

4/5 take away 4/5 is equal to zero.

How did you do? Hopefully, you also came up with some maths stories for these too.

If you'd like to share any of your maths stories, please ask your parents' or carers' permission and you can tag us using the information below.

Now it's time to complete the quiz.

Thanks very much.

Take care.