Lesson video

Hello, my name is Miss Robson.

In this lesson, we are going to be looking at how to subtract by partitioning.

First, we're going to look at partitioning a number to subtract.

Then we're going to complete the talk task first together, and then you by yourself.

Then we're going to look at how to write subtraction equations, before it's time for you to complete the independent task and your quiz.

For this lesson, you will need a pencil, some paper, and some objects for counting.

Pause the video here to collect the items that you need and when you're ready, press play.

We're going to start this lesson like we've started many of our lessons in this unit by practising our number bonds.

Today, we're going to be practising our number bonds to seven, and you can see lots of towers of cubes using two different colours to represent the different parts of the number bonds.

The first tower has seven red cubes and zero yellow cubes.

So seven and zero makes seven.

The next tower has six red cubes and one yellow cube.

So the missing number for that equation would be one, six plus one equals seven.

Six and one makes seven.

Pause the video here to complete the rest of the missing numbers and when you're ready, press play, and we'll go through the answers together.

You ready to go through them together? Remember, please join in with the full sentences, you can join in after you've heard a few if that helps you to.

Seven plus zero equals seven.

Oh sorry, seven and zero make seven.

Six and one make seven.

Five and two make seven.

Four and three make seven.

Three and four make seven.

Two and five make seven.

One and six make seven.

And zero and seven make seven.

Whoever has arranged these cubes like this has done this systematically because if you look down the left hand column, you can see seven, six, five, four, three, two, one, zero like a count down.

And then let the other side, you can see counting up zero, one, two, three, four, five, six, seven.

So they've worked one by one, moving the cubes, almost creating stairs using the red cubes.

And working systematically through them to make sure that they've covered all of the number bonds.

We're going to look again today at the elves.

I can see that there are five elves standing up and two elves sitting down.

We've looked at this before for addition and we've said that five plus two is equal to seven, five and two more make seven.

Today we're going to think about it in the context of subtraction.

So there are seven elves all together.

Count with me just to check one, two, three, four, five, six, seven, seven all together.

This time, we are going to be subtracting from the whole.

So the whole is seven, and we're going to take away the two elves that are sitting down.

So we're only thinking now about the elves that are standing up.

What we did there was we partitioned the two groups, which means we broke it into two groups.

So we had one, two, three, four, five standing up and six, seven sitting down the two sitting down at the end.

And we said, we don't need them anymore, we're thinking about the elves that are standing up now.

So I took away the two and I popped it somewhere else and I've just got seven left.

When we had the five elves standing up and the two elves sitting down, all together we have seven elves.

This time we were thinking about the seven as the whole, so seven elves all together, and then two of them sat down so there were five elves left standing up.

What do you notice is the same and different about these equations? Pause the video to have a look and see what you think is the same or different about the equations.

I've noticed that in both equations I have the same numbers.

So I have five and two as a part, five and two as a part.

And over here in the part whole model, five and two as a part.

I've also noticed that the whole is always seven.

So the whole, I can see in a blue square here, seven, seven, and seven.

The difference is that when we add things together, we get the two parts and we put them together to make the whole.

And when we subtract, we start with the whole and we take something away.

That's our partitioning, breaking it into two groups.

So we start with the whole, and we take something away.

The difference between addition and subtraction is that when we add things together, so five and two, we have a whole of seven which is bigger than the parts.

When we subtract, we start with the whole, so we start with the biggest part and we take away something else.

So this time, I've taken away the part of two, and I'm left with my other part.

If you look at the part whole model, I started with seven, which is the whole on my part whole model, I took away two, which meant that I was left with five, which is the other part in the part whole model.

All three of these representations, both the addition, the subtraction, and the part whole model use the numbers seven, five and two, but they use them in slightly different ways.

Your talk task is going to be to practise partitioning some different numbers.

So choose any number up to 10.

As you can see with my cubes, I've chosen to use the number eight.

And what you're going to do is you're going to partition that group somehow.

So I'm going to use my pencil, are you ready? I'm going to chop the group into two different parts.

So I had one, two, three, four, five, six, seven, eight cubes all together, and I've chopped it so that I have two different parts.

Now I'm going to move one part to one of my parts, and I'm going to move the other part to the other part.

I started with eight cubes, I partitioned and I took away three and I was left with the remaining part, which is five.

So I know that eight take away three is equal to five.

Watch that again with my cubes.

So I partitioned the eight by popping my pencil in the middle of the part whole model, and I moved them into the other part.

Three is a part, eight take away three is equal to five.

When I had all eight together in the whole, I took away the three and I was left with the remaining five.

You are going to have a go with your part whole model and your countable objects, whether they're cubes, beads, buttons, or whatever, at gathering them in the whole.

You can use your hand or a pencil to chop that into two pieces and push some of them into the first part, taking them away, and finding out how many you're left with in your second part.

I've also had a go at writing the equation.

I had eight all together, I took away three and I was left with five.

You can have a go at writing the equation too.

Pause the video here to complete your talk task.

When you've completed a few different partitionings of different groups within 10, and you've either said or written down some equations, you can press play.

Let me show you a few more subtraction stories.

Now it's time for you to complete the Independent Task.

The Independent Task is about Snow White.

Let me read you the text on the screen.

Snow White is trying to figure out how many dwarves might be late for dinner and might have to eat their food cold.

What if one dwarf is late? What if two dwarves are late? Using the part whole model, work through all of the possibilities, recording the equation and explaining what each part of the equation means each time.

So you are going to start with eight in your hole.

That is going to be one Snow White and seven dwarves in the whole.

And each time you have to ask yourself, "What happens if one dwarf is late?" If one dwarf is late, that means seven people will be able to eat their food hot.

So I've taken away one, I've put that in one of my parts and I'm left with seven.

Eight take away one is equal to seven.

The one is the dwarf that's going to be eating cold food.

And the seven is the dwarves and Snow White who are going to be eating hot food.

Eight was how many people there were all together possibly coming to dinner.

Then I talked to myself about the second option.

What if two dwarves are late? I've got eight all together, eight possible people could attend my dinner, this time two dwarves are late and they're going to eat cold food.

So eight takeaway two, six dwarves will be able to eat warm food.

Eight take away two is six.

Two is the amount of dwarves who are late, six is the amount of dwarves and Snow White who are going to be eating a hot dinner.

And eight was how many people all together could have come to dinner.

You need to have a go at working through what if one dwarf was late? What if two, or three, or four, or five, or six, or all seven dwarves were late? Talking each time about what different parts of the equation mean? And you're using your cubes to represent the different parts.

Now it's time for you to pause the video and complete your Independent Task.

Remember, you're trying to tell different stories about all eight guests that Snow White is cooking for and how maybe one, two, or three of them are going to be late.

So you take those away from the whole to find out how many of the guests are going to be on time.

Pause the video here to complete your task, and when you're finished, press play.

What interesting math stories did you manage to come up with? Would you like to share them with us? If you would, please ask your parent or carer to share your work on Instagram, Facebook, or Twitter by tagging @OakNational and using the hashtag #LearnwithOak.

We'd love to see what you've been getting up to.

Thanks for joining me today for this lesson on partitioning to subtract.

I hope that you've had as much fun telling math stories as I have.

Don't forget to go and complete the quiz.

Thanks again for joining me, see you next time.