Lesson video

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

Today we'll be solving addition and subtraction word problems. So on our lesson agenda, it looks like first we'll be creating bar models.

Then we'll be matching those bar models to word problems. Then we'll be solving the word problems. And finally, you'll be off for your independent task.

For this lesson, you'll need a pencil and notebook.

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

Super, let's get started.

So, it looks like in our photo, the builders are really hard at work.

And let's see what it says.

The builders were expecting a delivery of 73 bricks, however, only 51 were delivered.

How many bricks are they missing? Well, whenever we have a word problem, we have to ask ourselves two really important questions.

What do we know? What do we not know? What do we need to figure out? So, what do we know? Well, we know the builders were expecting a delivery of 73, but only 51 were delivered.

So they needed 73 delivered, they were expecting that, but only 51, a part of that, got delivered.

So I think I know my whole.

I know my whole is 73 because that's what they were expecting, but they received only a part of that.

So that's another thing I know.

I know one of my parts is 51.

What I don't know is how many they're missing.

That's what I need to figure out, so that's my unknown.

That's what I don't know.

So, I have my whole, I have one of my parts, but I need to find my other part.

And the way I've done this, is I've created a bar model where my whole is the bigger piece, and then my parts are the smaller pieces.

So, let's have a look at another word problem.

So, it looks like in this word problem, Sally built a wall using 48 bricks.

Bob built a wall using 35 bricks.

How many more bricks did Sally use? Okay, so let's ask ourselves, what do we know? Well, we know that Sally built a wall using 48 bricks, and Bob built a wall using 35, so a little bit less than Sally.

How many more bricks did Sally use? So I know Sally used more bricks, that must be my whole because I want to know how many more bricks did she use.

So I know my whole, I know Sally used 48, and I know that Bob only used a part of that, he only used 35.

So again, in my bar model, my whole is 45, is 48, sorry, my whole is 48, and one of my parts is 35.

What do I not know though? Ah, I don't know my other part.

I don't know how many more bricks Sally actually used.

So that's what I need to figure out.

So in my bar model, that's the missing piece, is one of my parts.

Super, so, in our talk test today, we're actually going to do some exploring.

So what I'd like for you to do is I'd like for you to match the bar model to the word problem.

So, I'll start with the word problem here.

I'll start with D.

So I'm not going to start from the beginning, I'll start with the end.

So it looks like in D, the builders had 74 bricks this morning, they used 57.

How many bricks do they have left? Okay, what do I know? I know they had 74 bricks this morning, and then they used 57.

So they started with 74, that's my whole, and they used a part of that, so 57 is one of my parts.

So which of these bar models will match where 74 is my whole, and 57 is a part? Oh, I think that first bar model matches.

They had 74 as the whole, they used 57, and then we don't know the missing part, we don't know how many are left.

So, your turn.

Match the bar model to the word problem.

And when you're ready you can resume the video, and we can go over the answers.

So pause now, good luck.

Super.

So hopefully you completed your top task and you figured out that this bar model belonged with C, because it looks like in C, Bob drove 56 miles to work, whereas Sally drove 38, and we need to figure out how many more miles Bob drove.

So Bob was the whole, and Sally only drove a part of what Bob drove.

This bar model matched B because Sally had 41 pipes and Bob has 26.

How many more pipes does Sally have? Sally had the whole, and Bob only had a part of what Sally had, and we need to figure out the difference between them.

And it looks like this last bar model matched A, 36 builders were building, 29 were driving diggers.

How many builders were there altogether? So it looks like we add the 36 and the 29, and then we can find our whole.

So we had the two parts, but we were missing the whole.

Great.

So, now let's have a look.

I know that our unknown in the first word problem was the part, because they were expecting 73 bricks, but they only had 51 delivered.

So how can we solve for the missing piece? Hm.

Well, I know that when I have a whole and one part, but I'm missing the other part, I need to subtract from the whole.

So I need to subtract, 73 minus 51, and whatever I have left, is my missing piece.

So, 73 minus 51, how can I solve this? What strategy would you use? Well, I would just partition the second number into five, tens, and one, one, or actually, no, I wouldn't, I would round and adjust, because 51 is only one away from 50.

So I would round to 50, and then adjust.

So 73 minus 50, so 7 minus 5 is equal to 2.

So 73 minus 50 is equal to 23, and then I need to minus, I need to subtract one more.

So 23 minus 1 is equal to 22.

So, that's my missing piece, is 22.

Let's try solving our other word problem.

Now remember, in this word problem, Sally built a wall using 48 bricks.

So she used more than Bob, so that was the whole, and Bob only used a part of what Sally used, he only used 35.

And we want to know how many more, how many more bricks did Sally use? So again, if we have the whole and the one part, we can subtract from the whole to find the missing part.

So here we subtract 48 minus 35.

How should we solve this? What subtraction strategy do you think we should use? If you have a good guess, pause the video and solve it.

If you're not too sure, just stay on with me.

So I think this time I will partition 35 into three tens, and five ones.

So 48 minus 30.

Well, I know 4 minus 3 is equal to 10.

So 48 minus 30, 48 minus 30 is equal to 18, and I still need to subtract another 5.

Okay, 18 minus 5.

I know 8 minus 5 is equal to 3.

So 18 minus 5 must be equal to 13.

Super.

So we're already ready for your independent task.

For your independent task, I'd like you to solve the following word problems that we looked at during our talk task when we explored.

So again, you can use any strategy you think is appropriate to solve.

So I remembered that for A, okay, that matched this bar model here, where we know our parts, but we don't know our whole.

So that must mean we need to add our parts to find our whole.

Okay, 36 plus 29.

Okay, how do I solve 36 plus 29.

I think I'll round and adjust.

So I'll round 29 to 30, 36 plus 30, 3 plus 3 is equal to 6.

So 36 plus 30 is equal to 66, and then I need to subtract 1 to adjust.

So 66 minus 1 is equal to 65.

Your turn, solve the rest of the word problems. And when you're finished, you can resume the video and we can go over the answers together.

So pause now, and good luck.

Super.

So, let's go over the answers.

In B, we have to subtract 41 minus 26, which is equal to 15, in C we have to subtract again.

56 minus 38 is equal to 18.

And in D we had to subtract again.

74 minus 57 is equal to 17.

Great job, everyone, those were some tricky ones.

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

As always, don't forget to complete your final quiz.

That was a really good effort from all of you, and I really hope to see you in future lessons, bye.