Lesson video

Hello, my name's Mrs. Cornwell, and I'm going to be helping you with your learning today.

I'm really looking forward to today's lesson.

I know you're going to work really hard and will do really well, so let's get started.

Welcome to today's lesson, which is called Find the missing part of an addition story, and it comes from the unit Additive Structures: Addition and Subtraction.

Okay, so in today's lesson, we're going to look at how we can find the missing part of a first, then, now addition story.

Okay, so let's get started.

So our keywords today are first, my turn, first, your turn.

Then, my turn, then, your turn.

Add, my turn, add, your turn.

And increased, my turn, increased, your turn.

Well done, excellent.

So in the first part of our lesson today, we're going to find the missing part of a first, then, now story when the first part is missing.

We'll find out how to do that.

In this lesson, you will meet Aisha and Alex, they'll help us with our learning.

So Alex has told a first, then, now story, but he has hidden one part.

Okay, so we can't see that first part.

Aisha tries to find the missing part.

Let's help her.

Collect some pencils and act out the story to find out how many pencils are in the pot at the start of the story.

We can tell the story to help us.

So we don't know how many pencils were in the pot at first.

Then, I put two more pencils in the pot.

Now, there are six pencils in the pot.

So if we were writing an equation to represent that, we would have to write a box for the missing number then plus two, because we know two was added, is equal to six, which is the amount at the end of the story.

At the end of the story, there were six pencils.

This was because we'd added two pencils to the pot, hadn't we? So we had six, but only because we'd added two.

So to find the number of pencils at the start of the story, I must take the pencils I added back out of the pot.

So Aisha said there must have been four pencils at the start of the story.

And there, we were right.

Let's use a picture to tell this story.

So we don't know how many there were at first, then four counters were added.

Now, there are seven counters on the tens frame.

So now let's write the equation.

So we write a box for the missing number.

Plus four is equal to seven, mm plus four is equal to seven.

At the end of the story, there were seven counters on the tens frame.

This was because we had added four counters to the tens frame.

So to find out how many counters were at the start of the story, I must take the counters I added back off.

And there we are.

We can see that there were three counters at the start of the story, can't we? Let's draw the counters there and we can fill in the three in the box to show that that was the missing number in the equation, the missing first part.

So now it's time to check your understanding of that, tell the story and draw the missing first part.

Okay, so you can draw the counters like we did and write the equation.

So pause the video now while you try that.

And let's see how we got on.

So we don't know how many counters there were at first.

Then three counters were added.

So now there are nine counters on the tens frame.

So what did we have to do to find out how many there were at first? Okay, so we must take the three we added from the end of the story, mustn't we? So let's write the equation.

Mm plus three is equal to nine.

So we can see that if we take off the counters that were added, we take off the three from the nine.

There must have been six counters at the start of the story.

So, well done if you did that.

So Alex wants to find the number at the start of this story.

And there's an equation there underneath as well, isn't it? Mm plus two is equal to five.

Okay, and he says, "Two counters were added to the number at the start, so to find the missing part, I will add two and five." What mistake has been made? Should he add two and five do you think? That's right, two counters were added to reach the whole amount of five.

So we must take the counters away from five to return to the start of the story.

So we can see here, two was added to the missing number to reach five.

So we can see that two must have been added there like that.

And so you need to take them back off to find out what the missing number was, and we can see that it is three.

And so we can draw those counters at the start of the story, can't we? Okay, so Alex has got a problem here then.

He's saying that Alex wants to find the equation to represent the story shown here.

Okay, so let's help him.

So we can see there are two equations.

One of them says mm plus three is equal to seven, and the other one says mm plus three is equal to 10.

Okay, so let's think about what that story shows.

So we can see mm is the missing part, the first part, and then it says plus three.

So we can see there's three counters there that are being added.

And then we can see at the end of the story, there are seven counters.

Okay, so it must be mm plus three is equal to seven.

That's right, well done.

And we can see that the missing number was four, because we had seven at the end of the story, didn't we? We must have added three to the missing part to reach seven.

So we take three back off seven to get back to the missing part, so well done.

And there, we can see the missing part is four.

Okay, so now it's time to check your understanding.

Find the equation to represent the story, then solve it.

Okay, so there's a story there, and you have three options.

A is mm plus six is equal to 10, B is mm plus two is equal to six, and C is mm plus four is equal to 10.

So pause the video now while you try that.

Okay, so let's see how you got on.

So which equation did you think was correct to represent that story? That's right, B.

Mm plus two is equal to six, because we can see, we don't know how many are in the missing part at the start of the story, but two were added and it reached the whole amount of six, didn't it? Okay and then let's think about how you'd solved it then, what did you do? So we know that two was added to the missing part to reach six.

So you need to take two from six to get back to the missing part, don't you? And so we know the missing part must have been four.

So well done.

Aisha wants to find out how many counters there were at the start of this story.

She says, "There were eight counters at the start of the story." Do you agree? Is that possible do you think? No, there couldn't have been eight counters at the start of the story, because there were only five at the end of the story.

And it's an addition story, isn't it? The number at the start of the story is increased in an addition story.

So the amount at the end must be greater when you're working with counters and real objects.

The story must have started with a number less than five.

And there we can see in this case, it started with two, didn't it? Okay, so time to check your understanding again.

Which of the following numbers could not be at the start of this story? Okay, so you've got three options, you can see the story there, can't you? And the equation says mm plus three is equal to seven.

Okay, and then the possible options are A, seven, B, four, or C, eight.

So pause the video now whilst you think about which one of those numbers could not be at the start of that addition story.

So let's see how you got on there then.

What did you think? So that's right.

Seven couldn't be at the start of that story.

And because if you start with seven and some more are added, you won't end with seven, will you? And also eight couldn't be at the start of that story, because if you start with eight and add some more, then you can't stop, you can't end with seven, can you? Because the amount cannot decrease when you add more.

So, well done.

The number at the start of the story was increased, so the amount at the end must be greater.

Okay, so here's your task for the first part of today's lesson.

Find the missing first part in each story and equation.

Okay, so have a look at that and you're going to fill in the missing number in the equation, okay? Remember, tell the story to help you and you might want to use objects to help you as well.

And here's the second part of our task, okay? So work with a partner and then Alex is telling us what to do.

"We will each make up a story with the first part missing and draw it on the storyboard." "Then we will swap our stories and use a tens frame to solve them." So you won't draw the first part on, because that's the missing part.

But you will draw how many were added and how many are at the end.

And you could use counters to help you as well, couldn't you? Okay, remember to write the missing equation to match your story.

So pause the video now while you do that.

Okay, so let's see how you got on.

Find the missing first part in each story and equation.

Okay, so if we tell the first story, first, we don't know how many cakes were on the plate, but when two were added, then it reached three cakes at the end of the story, didn't it? Okay, so if we had two added to get to three, we have to take the two back off and we can see that it will get us to one, won't it? So one plus two is equal to three.

There must have been one at the start of the story.

So let's look at this next picture.

We can see there are four balls at the end of the story, but to get to four, two were added.

So to get back to the start again, we have to take those two back off, don't we? Okay, so if we take the two back off the four, there must have been two at the start of the story.

There we are, two plus two is equal to four.

And then let's look at the last picture.

Okay, so we can see that there were five eggs at the start, at the end of the story, sorry.

And we got to that five by adding two.

So we need to take the two back off, don't we, to get back to the start of the story, so we can see that there must have been three at the start.

There we go.

Three plus two is equal to five, so well done.

So let's see what you did in the second part of the task.

You may have done this.

Alex is telling us there, "I ended my story with seven counters and showed that I had added two to the start." Okay, so there's seven at the end, and he showed that he'd added two.

And then Aisha said, "I knew I must take two counters from the amount at the end of the story." Okay, so we ended with seven.

So if you take two back off again, then there must have been five counters at the start of the story.

And we can see mm plus two is equal to seven.

Five plus two is equal to seven, isn't it? So, well done.

And there, we draw the five counters on as well to show that, don't we? So, well done, you've worked really hard in the first part of our lesson today.

So the second part of our lesson is when we're going to find the missing part when the then part is missing.

So collect some coins and act out the story to find the missing part.

What is different about the missing part in this story? That's right.

This time, the then part of the story is missing.

First, there were three coins in the piggy bank, then, we don't know what happened, we don't know how many were added.

But now there are six coins in the piggy bank.

And Aisha's saying, "I noticed that the number at the start increased." So, we know it's an addition story.

That means some coins have been added.

At the start of the story, there were three coins.

At the end of the story, there were six coins.

Let's represent this as an equation.

Okay, so we'll have three plus, and then we need a box for the missing number.

Three plus mm is equal to six.

I know six is the whole amount at the end of the story, and three is a part, so the other part must be three.

Three coins were added.

Let's use the picture to tell this story.

First, there were three counters on the tens frame, then, we don't know what happened.

Now, there are five counters on the tens frame.

Let's represent this as an equation.

Three plus mm is equal to five.

Draw the part that was added.

So I know five is the whole amount at the end of the story, and three is the first part.

So, the missing part must be two.

There we go.

Three plus two is equal to five.

So, now it's time to check your understanding again.

Which equation represents this story? So, there's A, one plus mm is equal to four, B, four minus mm is equal to three, or C, three plus mm is equal to four.

So, pause the video now while you try that.

Okay, and let's see how we got on.

So, what did we think? We can see that three plus mm is equal to four, because we've got three cakes at the start of the story there.

Okay, and we don't know how many were added, so we need a box for that missing number.

Okay, but there were four cakes at the end of the story.

And then we know that it will be three plus one is equal to four, because when four is the whole, three is a part and one is a part, and there it is.

Let's think about whether Aisha could be right.

So she's saying here, "I think that seven counters were added." Okay, so we've got a story here and we have to think, could she be right? Could seven counters have been added? So there were four counters at the start of the story.

There were six counters at the end of the story.

There could not have been seven counters added, could there? Because the number added must be less than the whole amount at the end of the story.

And there, we can see in this case, two were added.

Okay, so here's the task for the second part of today's lesson.

Okay, so you've got some stories there, first, then, now stories.

Okay, and it says complete the missing part in each story and equation.

Okay, so we've got three plus mm is equal to five, five plus mm is equal to seven, and two plus mm is equal to six.

And then the second part of your task here is work with a partner again like Alex and Aisha.

And Alex is telling us what to do.

"We will each make up a story with the then part missing and draw it on the story frame." "Then we will swap our stories and use a tens frame to solve them." Remember to write the missing number equation to match your story.

Okay, so pause the video now while you do that.

Okay, so let's see how you got on in the first part of your task.

Okay, so we can see here, we've got a picture of the cakes, haven't we? First, there were three cakes on the plate, then, mm was added, and now we know we ended up with five cakes on the plate.

So three plus mm is equal to five.

So we know that five is the whole amount at the end of the story.

And we know if three is a part, then the other part must be, that's right, two, excellent.

Okay, and then this next picture here, this next story.

Okay, so we can see first, there were three eggs in the egg box, then mm eggs were added.

Okay, we don't know how many eggs were added, but at the end of the story, there were six eggs in the egg box.

Okay, so the end of the story has the whole amount, doesn't it? There were six in the whole.

So if three is a part, then the other part must be three.

That's right.

Okay, and then the story at the end here, we can see that we had three First, there were three balls in the box.

Okay, we don't know how many were added, but at the end of the story, there were seven balls in the box.

So we know that if seven is the whole and three is a part, then the other part must be, that's right, four.

So, well done, excellent.

So now let's look at the second part of your task.

So you may have done this, here's an example.

So you may have started your story like Alex, "I started my story with four counters and ended it with nine counters." Okay, so he drew what was at the start of the story and what was at the end of the story.

And then Aisha was solving it.

She said, "I knew that nine is the whole, and if four is a part, the missing part must be five." So there's four is a part, the missing part is five there.

Okay, and then remember to write the missing number equation to match your story.

So it would be four plus mm is equal to nine.

And then we found out the missing part was five, didn't we? So, well done, you've worked really hard and now hopefully you feel much more confident about how to find the missing number in a story or equation.

Okay, so let's look at what we've learned in today's lesson then.

When we know two parts of a first, then, now story, we can find the missing part.

In an addition story, the number at the start of the story cannot be greater than the number at the end of the story.

And in an addition story, the number added cannot be greater than the whole amount.

Okay, so well done, you've worked really hard today and I've really enjoyed today's lesson.