Lesson video

Good morning, it's Miss.

Brinkworth here again with Oak National Academy, really excited to be carrying on your fraction work with you today.

So, our learning objective for today.

What we're going to be looking at is to subtract fractions with the same denominator.

So, as usual, just make sure you've got a pen, a pen or pencil and something to write on.

Pause the video here if you need to go and get that.

And also, make sure you've done that introductory quiz, which has some nice revision on yesterday's adding fractions learning.

So, if you haven't done this already, please pause the video here and have a go at that introductory quiz.

Okay, let's have a bit of a warmup then.

Now, here's an adding fractions question but someone's made a mistake.

Pause the video.

Can you see what that mistake is and can you write the correct answer? They've made a mistake in that working out.

2/4 add 1/4, they've written 3/8.

What mistake have they made? Pause the video and have a go.

Obviously, we know that when you are adding fractions, the denominator doesn't change.

As long as the denominators are the same, the denominator doesn't change, we don't add that section of the fraction together.

So, the correct answer this question of 1/4 add 2/4, 2/4 add 1/4, it doesn't matter which order we do them in, is 3/4.

Well done, if you remember that from yesterday.

Okay, let's move on.

Nice big tick if you remember that from yesterday.

We've got our star words here.

I'm going to say the star words and you're going to repeat them at home, okay? So, we've got fraction, denominator, numerator, subtract, whole, minus.

And we can see that a lot these words are reappearing each day, with denominator and numerator, whole and fraction.

But new for today is that subtract and minus because that's our learning for today, we're going to be subtracting fractions with the same denominator.

Okay.

What's being shown here then? What have we got? What do you think our denominator will be for this question? Remember that to work out the nominator when we have a shape question like this, we just count how many equal parts in total the shape has been split into.

Now, be careful cause what people sometimes do is just count the coloured sections.

It's the total equal sections that we need to count.

So, how many equal sections has the sheet been cut into? It's been split into four equal sections.

So, our denominator for this question will be four, and that won't change.

Okay.

So, how many coloured sections have we got? Remember that becomes your numerator.

So, in that first square, we have three coloured sections, that's our numerator.

We've got three.

We've got 3/4 represented in that first shape.

In the second shape, we can see that that's changed.

We've got 3/4 at the beginning, but two of those quarters have now turned white.

So, we've got 3/4 at the beginning, but now, two of those quarters have been taken away.

So, if we do 3/4 take away 2/4, looking at the square there at the bottom left, how many quarters are we left with, how many green sections are left? We started with three, two have been taken away, how many are we left with? Well, we are left with 1/4.

And here's our learning for today, three take away two, is one, you know that subtraction fact.

And so, today to subtract fractions with the same denominator, you just subtract the numerators.

Three take away two is one.

And you can use your addition facts to help you with subtraction questions.

So, you know, two add one is three.

And so, when we're doing a question like this, then we can see that that missing number, we've got three and we take away two, the missing number in that equation is one.

Here's the same equation shown a slightly different way.

3/4 take away 1/4 is 2/4.

We've moved the numbers around but we're using the same mathematical facts to help us answer that question.

Now, the numerator changes not the denominator.

We can see very clearly in that question at the top that the denominator remained four, and it's just the numerator that changes.

Like with all subtraction questions, we would expect our answer to be smaller than the question we started with.

When we subtract numbers, they get smaller.

Just like yesterday, our answers were getting bigger when we were adding.

They should be getting smaller today when we're subtracting.

The order is important when subtracting, and this is because we know that seven take away two is not the same as two take away seven.

So, do you think carefully about your order? This question up here at the top, the order has changed, and so, the answer has changed slightly.

Okay, let's move on.

Why don't we subtract the denominator? Well, because we can see that six, six take away two, six, the correct answer is 4/6.

The answer at the bottom there is not correct because somebody's made the mistake of subtracting the denominator.

Don't make that mistake in your work today, okay? This is because if we look at this circle, the denominator hasn't changed, the circle is still split up into six equal parts.

All we're doing is talking about subtracting some.

So, please don't make the mistake of changing the denominator, leave the denominator as it is for today's work.

Okay.

So, looking again at that part whole model that we introduced yesterday, and it will help us with today's learning as well.

So, this shape is cut into five equal pieces in total, five equal pieces in total, 5/5.

If we, for example, say, "Well, what if we take away the yellow sections?" There are three yellow.

So, that's 3/5.

5/5 take away 3/5 is, 2/5.

We're left just with the red section and they represent 2/5.

5/5 take away 3/5 is 2/5, exactly the same way as 5/5 take away 2/5 would be 3/5, it's just the other side of that fact.

And you can see that you can use your addition knowledge to help you with the subtraction questions today.

Okay.

Let's have another go then.

Let's have a look at how much this has been split into.

Well, the question already tells you that the denominator is nine.

So, there are nine equal parts in total.

Seven of them are coloured, two of them are coloured slightly differently.

So, seven take away two.

Seven take away two is five.

5/9, 7/9, take away 2/9 is 5/9.

And you know that because you know that seven take away five is two and you can work that all on your fingers or whichever way you normally do that if you don't know that fact.

Okay.

What about this part whole model then? Have a look at what's being shown here.

You've got 7/9 and out of that 7/9, some have been coloured differently.

So, 7/9, I know that seven take away four is three, I can see that there are four of those, sections have been coloured differently to the others.

Seven take away four is three.

So, my missing part of my part whole model, seven is made up of three and four.

So, I know that if I take four away from seven, I end up with three, 3/9.

Just have a look at that to make sure that you understand what's happened there.

We started with seven, seven coloured sections in total, we took those four darker ones away, and so, we're left with three.

Okay.

Your turn, I'd like you to use the part whole model if you can, to answer these questions.

We've started, the first one has been, you've been given the whole of 4/6, but have a look at the other questions carefully to make sure you know what you're taking away.

So, pause the video here and have a go at those questions.

If we just have a look at the first one together, it says, 4/6 take away 1/6.

Well, I know that four take away one is three.

So, my answer will be 3/6.

Pause the video and have a go just at those last two questions.

Read the question carefully to make sure you know how many you're starting with.

Okay.

Let's have a look at these together.

We've got six take away four, six take away four is two, and we know that the denominator doesn't change.

So, that seven stays the same, 2/7.

So, the last question we've got three take away two is one, 1/5.

Well done, if you got all those questions correct, really good work.

Okay, we're moving on to the independent work here.

I will just have a look at the first question with you.

So, this is what your independent work looks like today.

You have fractions and for the first page, you have whole fractions that you're subtracting.

Okay? So, we've got 8/8 and 9/9, et cetera, you've got those whole fractions that you're subtracting a number from.

So, having a look at that first question, 8/8 take away 4/8.

So, the math that I need to do, the subtraction question I need to think about, is eight take away four, eight take away four is four, eight take away four is four.

So, 8/8 take away 4/8 is 4/8.

And if I want to think about checking that answer, I can see that four add four is eight.

And so, they add up to the original fraction.

So, that's how I can use my addition facts to help me with subtraction.

Have a go at the rest of the worksheet and we'll come back together in just a moment.

Okay.

Let's have a look at the end of these questions, the last of these questions together, b says 9/9 take away 8/9.

Well, nine take away eight, nine take away eight is one.

9/9 take away 8/9 is 1/9.

Okay, c.

Six take away two is four.

So, 6/6 take away 2/6 is 4/6.

And for the last question, eight take away two is, sorry, eight take six is two.

So, we end up 2/8 for that question.

Okay.

These, you haven't got the pictures to help you, but hopefully you can see the pattern that's being followed here and that you just need to subtract the numerators to get these answers.

So, for question one, seven take away four is three, 3/8 is your answer for that question.

Four take away three is one.

So, we've got 1/5 for question two.

Four take away three is one.

So, our right answer is 1/6.

We've got our tenths down here on question four, eight take away two is six, 6/10.

And for question five, we have to do something a little bit different, you have to work out what the denominator to the answer is going to be first.

Now, you know that the denominator doesn't change.

So, if we've got 6/7 and something sevenths, the denominator is always going to be seven.

But then, we need to think, "Right, what's happened to six if I've ended up with two?" What's happened to six if I've ended up with two, what have I taken away? I must've taken away four if I've ended up with two.

And really well done if you had to go at this challenge question.

If a shape is cut into nine equal pieces, and I gave four pieces to one friend and two pieces to another, how many pieces will I have left? This is a two step subtraction question.

So, really well done if you got onto this one, let's have a look at it together.

The important thing to do initially is to write down what you know.

Right.

I've got nine equal pieces and I've got all nine of them at the beginning of this question.

So, 9/9.

Now, I know I'm going to take away because I'm giving some of that shape to my friend, I'm giving it away, I'm taking it away, I'm going to end up with less.

So, how much have I given to my friend? I've given four pieces, right.

Four pieces is 4/9.

Going to answer that question then, then 9/9 take away 4/9, I get 5/9.

Well done if that's how far you got, that's great, but that's not the question finished because it's a two step question.

It then says that I give two pieces to another friend, aren't I generous? So, I get my 5/9 and I've got to take away again, I've got to take another 2/9, which I give to another friend.

Five take away two is three.

Really, really good work Year Three if you got all the way to that correct answer as 3/9.

Fantastic.

Right, pause the video here, have a go at that final knowledge quiz, just going to see how well that learning's gone in for today.

Brilliant work guys.

Very, very hard work done there for subtracting questions.

Really, really good.

Have a great day, bye bye.