# Lesson video

In progress...

Hi, everyone, I'm Miss Mitchell.

Today, we're going to be representing two-step word problems using a bar model, so go and get yourself ready.

In today's lesson, we'll be representing two-step word problems using bar models.

We'll be drawing bar models.

Then I'd like you to complete the worksheet and then a quiz For today's lesson, you will need a pencil, a ruler and some paper.

Pause this video now to get this, if you have not got it already.

Class 2A have 42 gold stars.

The boys won 13 more gold stars.

The girls won 22 more gold stars.

How many gold stars do Class 2A have now? How can I represent the maths in this word problem using a bar model? What are the values of my parts? What is unknown? In this question, I can see that I have one part of 42, because they won 42 gold stars.

They won 13 more, so this 13 is another part.

But then, the girls won 22 more, so there's a third part.

I know that there are three parts, but the whole is the unknown value.

What operation will I be using? Addition.

When I need to find out the whole, I add the three parts together.

What equation or equations need to be done in order to solve the problem? Pause the video now to see if you can work out the problem.

There are many different ways that you could solve this problem.

You could do 42 plus 13 plus 22, which is equal to 77.

So in this method, you were adding three parts together, all at the same time.

For example, you could do 42 plus 13, which is equal to 55, and then you could do 22 plus 55, which equal to 77.

Or you might have done 42 plus 22, which is equal to 64, and then 64 plus 13, which is equal to 77.

Or you might have done 22 plus 13, which is equal to 35, and then 35 plus 42, which is equal to 77.

You need to find the easiest way that works for you.

Did you notice that the different calculations led to the same answer? It didn't matter which order the parts were added.

The answers are always the same.

Does this always happen? Does it matter which order I add the parts? No, when you are adding, it can be in any order.

Let's try a new one.

Class 2A have 21 gold stars.

The boys then won another 15 gold stars and the girls won another 13 gold stars.

How many gold stars do Class 2A have now? Hmm, what is known and what is unknown here? How can we use that information to represent this problem as a bar model? Pause the video now to have a go.

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

What do I know? Well, I know that Class 2A started with 21 gold stars, and we can represent that like this.

I know, then, that the boys won another 15, so I need to add a bar onto this and label it 15.

And then that the girls won another 13 gold stars, so again, I'm going to add a bar on here and label it with a 13 this time.

Now what I do not know is how many they have now altogether.

My whole is unknown.

Okay, how can I use this information to now solve the problem? To solve it, I would add three parts together to get the whole, 21 plus 15 plus 13.

Again, there are many ways to solve this, but I like to add the three parts together at the same time, but I like to partition the tens and ones.

So 20 plus 10 plus 10 is equal to 40.

1 plus 5 plus 3 is equal to 9.

And 40 plus 9 is equal to 49.

So 21 plus 15 plus 13 is equal to 49.

The whole is 49.

Let's see if you can do this one by yourself.

Class 3G have 22 gold stars.

Kate won 16 more gold stars for the class.

Ben won 11 more gold stars for the class.

How many gold stars do Class 3G have now? Pause the video now.

Draw the bar model and write the equation to solve the word problem.

My first part is 22.

My second part is 16.

And my third part is 11.

I have three parts, but I don't know the whole.

Can you remember how to solve it? What will my equation be? That's right, 22 plus 16 plus 11 is equal to the unknown.

Again, solve it however is easiest for you.

I know that 2 plus 1 plus 1 is equal to 4.

So I know 20 plus 10 plus 10 is equal to 40.

2 plus 6 plus 1 is equal to 9.

40 plus 9 is equal to 49.

Great job guys.

Here's a different word problem.

The red table have 57 crayons.

Ben takes 12 crayons.

How many crayons are left? Now, what is known and what is unknown? Why is this question different to the others before? Let's take a look.

This is our whole.

But Ben takes 12 crayons from the 57, so he is taking a part.

This part here is the unknown.

So we know the whole, we know one part, we know another part, but the final part is unknown, and that's what we need to work out.

What calculation or calculations need to be done to solve this? My equation will be 57 take away 12 take away 14.

Pause the video.

How would you answer this question? There are different methods that you can use.

You need to find the easiest way that works for you.

You may have wanted to subtract one part and then the second part.

Like, 57 take away 12 is equal to 45, and then you do 45 take away 14 is equal to 31.

Or you may have wanted to add the two parts together and then subtract that from the whole.

So you could do 12 plus 14 is equal to 26, and then you take away from the whole.

57 take away 26 is equal to 31.

Could you now explain to me how you solved yours? That's great.

Yes, that's right.

Let's do one more before you do your worksheet.

The red table have 68 crayons.

Ben takes 11 of crayons.

How many crayons are left? Pause the video now to draw the bar model, which will help you write the equation.

The value of the whole is 68, so I draw my whole and label it.

One part is 11, so I split my bar and label it.

Another part is 13, which I can split and label.

But the final part here is the unknown value, which I also need to label.

What equation or equations needs to be done in order to solve the problem? Great, 68 take away 11 take away 13.

68 take away 11 take away 13 is equal to 44.

How did you solve it? Can you pause the video and explain to me how you solved this equation? Have a go answering these word problems. Draw bar models and label them, then work out the equation and solve it.

Pause the video now and then press play when you are ready for the answers.

Here is the answer for questions a and b, and here are the answers for questions c and d.

Great job.