# Lesson video

In progress...

Hello everyone, and welcome to maths with Ms. Dobrowoiski.

Today we'll be looking at solving addition and subtraction word problems. So let's have a look at our lesson agenda.

First, we'll be creating bar models.

Then we'll be matching bar models to word problems. Then we'll be solving word problems, and finally, you'll be ready for your independent task.

So for this lesson, you will need a pencil and notebook.

If you don't have these items, pause the video now and go get them.

Super.

Let's have a look at creating some bar models.

In the morning, the builder started with 52 bricks.

They used 17 bricks.

How many bricks did they have left at lunch time? Whenever we look at a word problem, we have to think, what do we know? What do we not know? To first represent this, I'm going to use a part-whole model.

That's what I'm going to use first.

Let's see if we can fill this.

So do I know my whole? In the morning the builder started with 52 bricks.

That's my whole, because that's what they've started with.

So I know they started with 52 bricks.

Hmm.

They used 17.

That's one of my parts because I don't know my other part.

I don't know how many they have left at lunchtime.

That's what I'm trying to figure out.

So in my part-whole model, 52 is my whole, 17 is my part, and we're looking for the other part.

Now, we can also represent this another way.

I know part-whole models are one way to do it, but let's have a look at another way we can represent this.

I know that my whole is 52.

I'm going to represent this using a bar model.

So there's my whole, they started with 52.

One of my parts is 17.

So there's my part.

And then the bit that's not filled in is my unknown.

It's what I don't know, so that's what I have to figure out.

My whole is 52 and I know one of my parts is 17.

So this is my bar model that I've created.

So the whole is always the bigger piece in a bar model, and the parts are always the smaller pieces that make up the whole.

Let's have a look at another one.

So again, the builders are really hard at work.

This time, Bob has 17 bricks and Sally has 32 bricks.

How many more bricks does Sally have than Bob? Hmm.

So I know Sally has more bricks, she has 32, Bob has 17, and I want to know how more bricks Sally has.

So do I know my whole? I know that my whole is 32 because I know Sally has more.

So I'm going to put 32 as my whole and 17 as my part.

And the missing bit is my other part.

See, the difference between what Bob has and what Sally has, is my missing part.

As you can see on my bar model, my whole is the biggest piece.

It's the biggest bit, Sally has 32, and my parts are the smaller bits that will make up the whole.

But right now I only know one part and not both.

Hmm, let's explore! My favourite.

So, as usual, I will do the first example and then you'll be off on your own.

For this let's explore task, I want you to match the word problems to the bar models.

You don't need to solve them, just match them.

So, I'll do A.

So, Bob, the builder, had 57 pipes.

Sally, the builder, had 25 pipes.

How many pipes did they have altogether? So let's see, what do I know? I know Bob has 57 and Sally has 25, but I don't know how many they have altogether.

So it looks like I know my parts, but I don't know my whole.

So that must match, uh.

That matches this bar model.

Bob has 57, Sally has 25, so these are my two parts, and what I'm looking for is the whole, because I don't know the whole.

Good, so now it's your turn.

Pause the video, match the bar models and the word problems, and when you're finished, resume the video so we can go over the answers, good luck.

Super, so let's go over the answers.

For B, Bob has 62 bricks and Sally has 14 fewer bricks.

Hmm, so that must match this one, because I want to know how many bricks Sally has.

Bob has 62, he has the whole, and Sally has 14 fewer, so we need to know how much Sally has.

Whatever Sally's part is plus 14 is equal to our whole.

For C, there were 73 builders on site, 26 were driving diggers and the rest were building houses.

How many were building houses? Well, there were 73, so that's my whole.

So it looks like this matches right up here.

73 is the whole, that's how many builders there are, 26 are diggers, so the difference between the two is my other part.

That's how many would be building.

Okay, and last but not least, Bob has 28 pipes and Sally has 41 pipes.

How many more pipes does Sally have than Bob? Well, I know that Bob has 28 and Sally has 41.

Sally has more, she has a greater value of pipes, so Sally has the whole.

Bob has 28, so that's one of the parts, and the difference between them would be my missing part.

That's how much more Sally has than Bob is the missing part.

Great job, everyone.

Now let's look back at the bar models we created and see if we can solve the word problems using our bar model.

So again, I know my whole is 52 because the builder started with 52 bricks, and my part is 17 because they used 17 bricks.

How many bricks did they have left at lunchtime? Well, if I know my whole and one of my parts, hmm, what calculation do I need here? I know my whole and one of my parts and I need to find the other part.

Oh, well, I'm going to use subtraction.

I'm going to subtract my part from my whole to find my other part.

52 minus 17.

What strategies do you use when you're subtracting? There's many different kinds you could use.

I personally really like partitioning the second number.

For example, 17 can be partitioned into 10 and seven.

So 52 minus 10 is equal to 42.

I know 42 minus two is equal to 40, so I'll partition the seven into two and five.

So 42 minus two is equal to 40, 40 minus five.

Hmm, I know 10 minus five is equal to five, so 40 minus five must be equal to 35.

Super, I was correct.

Now, let's try another one.

How many more bricks does Sally have than Bob? It looks like Sally has 32, she's got 32 bricks, Bob has 17, which is a part, and then the missing part is the difference between them.

So it's how much more Sally has.

If I know my whole and I know one part, but I don't know the other part, what operation do I need? What calculation do I need? Oh, I'm going to subtract from my whole.

So I have to subtract 17 from 32.

32 minus 17.

Now, again, if you'd like to, you can pause the video here and solve this equation on your own, but if you're not super sure, you could just listen to me and my explanation.

So again, I really like partitioning the second number.

That makes the most sense to me.

You might want to partition both numbers, but that's just the strategy I prefer.

I can partition 17 into one 10 and seven ones.

So 32 minus 10 is equal to 22, 22 minus two, I'm going to use the make-10 strategy now.

22 minus two is equal to 20, so I'll partition seven into two and five.

22 minus two is equal to 20, 20 minus five.

Well, I know 10 minus five is equal to five.

So 20 minus five must be equal to 15.

Super, I got that one right.

This always come so quickly.

For your independent task, I would like you to solve the word problems that we saw in our let's explore.

And you can use any strategy you think is appropriate for solving them.

So as usual, I'll do the first one and then you're off on your own.

So for A, Bob, the builder, had 57 pipes.

Sally, the builder, had 25 pipes.

How many pipes did they have altogether? Well, from looking at my bar model, I know I have two parts and I need to find my whole.

So I need to add 57 plus 25.

Again, I really like partitioning the second number, 57 plus 25, I know 25 can be partitioned into two tens and five ones.

57 plus 20 is equal to 77, 77 plus three is equal to 80.

So I'm going to partition the five into three and two.

77 plus three is equal to 80, 80 plus two is equal to 82.

Super, I got that one right.

Your turn, you go off, solve the equations, when you're done, resume the video and we can go over the answers together.

So pause now and see you when you're finished.

Great job, everyone.

So we already did A together.

B, 62 minus 14, because Bob has 62 bricks and Sally had 14 fewer.

So the missing piece is what we're looking for, and that was equal to 48.

For C, there were 73 builders, that was our whole, and 26 were driving so that's one of our parts.

How many builders were building the houses was the missing part.

So 73 minus 26 that were driving is equal to 47.

So 47 were building houses.

For D, Bob has 28 pipes and Sally has 41.

How many more pipes does Sally have been Bob? Well, it looks like Sally has 41.

So she has the whole minus how many Bob has, which is 28, would leave us with the difference, 13 pipes.

So Sally has 13 more than Bob.

Great job, everyone.

If you'd like to, you can share your work with Oak National by asking a parent or carer to share your work on Instagram, Facebook, or Twitter, tagging @OakNational and #LearnwithOak.

As usual, don't forget to complete your quiz.

It was really nice to see you and I hope to see you again for future lessons.

Bye.