Lesson video

Hi everyone, I'm Miss Mitchell.

In our math lesson today, we're going to be applying knowledge of lengths to word problems. In our lesson today, we're going to be looking at word problems. We will then complete a worksheet and then a quiz.

For today's lesson you will need a pencil and some paper.

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

Here, I have a word problem.

Johnny's arm is 45 centimetres long, and Anna's arm is 34 centimetres long.

What is the total length of both their arms? So we're looking for the total length.

So to solve this problem, I'm going to use the bar model to help me understand what operation I need to use.

So I know that Johnny's arm is 45 centimetres long, and Anna's is 34.

I'm looking for the total length, which means I'm looking for the whole and I know the two parts.

So I'm going to draw my bar model.

My first part is 45 centimetres.

And Anna's arm is 34 centimetres.

And I need to work out the total length.

The total length is what is unknown.

Now use this to work out what equation I need to do.

And my equation will be 34 plus 45, which is equal to the unknown.

I can then solve my equation.

45 plus 34 is equal to 79 centimetres.

So the whole is 79 centimetres.

I have a different word problem now.

Johnny's arm is 45 centimetres long, and Anna's arm is 34 centimetres long.

How much shorter is Anna's arm? So I'm looking for how much shorter Anna's arm is.

So what do we know and what is unknown? We know the length of Johnny's arm is 45 centimetres.

So you're going to draw your bar and label it 45 centimetres.

We know how much Anna's arm is, and Anna's arm is 34 centimetres.

What is unknown is how much shorter Anna's arm is.

But by looking at this bar model, I can see what my equation will be.

my equation will be 45 take away 34 to find out the unknown.

45 take away 34 is equal to 11.

Therefore Anna's arm is 11 centimetres shorter than Johnny's.

Let's try a new word problem.

Johnny had a plank of wood that measured 45 centimetres long.

He cut 34 centimetres off.

How long is the plank of wood now? So Johnny had a plank of wood that is measured 45 centimetres long.

He cut 34 off.

So what is unknown? We don't know how long it is now.

We know he started with 45 centimetres.

That is the whole 'cause that's what he started with.

And then he cut off a part of that.

And he cut off 34 centimetres.

What we don't know is how much is left? Now, by looking at this bar model, what calculation do I need to do to answer it? My calculation will be 45 take away 34 is equal to the unknown.

I can now solve my equation.

And 45 take away 34 is equal to 11.

Therefore he has 11 centimetres left.

Okay, let's try another one.

Johnny has a piece of ribbon measuring 78 centimetres.

He cut off 34 centimetres.

Then he cut off another 11 centimetres.

How long is the ribbon now? Can you pause the video to draw your bar model to work this out.

Press play when you're ready.

My equation will be 78 take away 34 take away 11, which is equal to the unknown.

That's because my whole was 78, a part was 34, which he cut off.

He then cut off 11.

And what was left was the unknown.

Did your bar model look like this? You can now use this bar model to solve the equation.

78 take away 34 take away 11 is equal to 33.

So the answer is 33.

Let's try a new one.

Anna knitted a scarf which was 44 centimetres long.

Then she knitted 34 more centimetres.

Finally, she knitted 11 centimetres more.

How long is the scarf now? Pause the video to see if you can work this out drawing a bar model.

Did you manage to find out the equation? It was 44 plus 34 plus 11.

We need to work out the whole.

The first part was 44 centimetres.

The second part was 34 centimetres.

And the third part was 11 centimetres And the whole was what was unknown.

You can now solve this equation.

44 plus 34 plus 11 is equal to 89.

So the whole is 89 centimetres.

It's now time for you to do your independent task.

Don't forget to write your units, whether it's in centimetres or metres.

Answer the word problems. And press play when you're ready for the answers.

Pause the video now.

And here were the answers.

Pause the video to check your answers are the same as mine.

You've worked really, really hard today, and well done for completing the lesson.

If you'd like to share you work with Oak National, please ask your parent or carer to share your work on Twitter tagging @OakNational and #LearnwithOak.

Now you've worked really hard, but let's see what you can remember by completing the quiz.

Well done for today, bye.