Lesson video

Hi, I'm Missus Dennett.

In this lesson, we're going to be looking at ratio.

We're going to be finding a part, given the value of a part of the ratio.

Tom and Mo share some money in the ratio 5:1.

Tom gets £80, how much does Mo get? We draw our bar model using the information we have been given to help us.

So we know that Tom gets five boxes and Mo gets one box.

All the boxes are equal in size.

We're told that Tom has got £80.

So the total of all of his boxes will be £80.

We want to find out how much Mo gets.

Tom has £80 shared equally between these five boxes.

This is 80 divided by five, which is equal to 16.

We put that in each box.

All of the boxes are equal.

So more get £16 pounds in his box as well.

So Mo has £16.

A drink of juice is made from cordial and water in a ratio 2:7.

Emma makes some juice using 357 millilitres of water.

How much cordial does she use? We have two equal boxes for cordial and seven equal boxes for water.

If we draw a bar model, what with that information do we have? Well, Emma is using 357 millilitres of water.

Now let's find out how much cordial she needs to use.

We share the 357 millilitres equally between the seven boxes.

That's 51 millilitres of water in each box, but also 51 millilitres in each box for cordial too.

This is because all the boxes are equal in size.

We can now find how much cordial is needed by multiplying 51 by two, which gives us 102 millilitres.

So Emma uses 102 millilitres of cordial.

Here's a question for you to try.

Pause the video to complete the task and restart when you are finished.

Here are the answers.

Emily gets 15 suites, which we share between her three boxes.

This tells us that there are five suites in every box.

So James has five suites in each of his seven boxes.

This is 35 suites.

Here's a question for you to try.

Remember, perimeter is the distance around a shape.

Pause the video to complete the task and restart when you have finished.

Here are the answers.

The smallest side of the triangle is represented by two parts or two boxes if you drew a bar model.

So we divide the length of the smallest side, 12 centimetres by two.

To find that each of the boxes or each part is worth six centimetres.

So the longest side will be six times six centimetres, which is 36 centimetres.

To find the perimeter, we need the lengths of all three sides of the triangle.

We know the longest side is 36 centimetres and the shortest side is 12 centimetres.

So we just need the length of the final side.

This is five times six centimetres of 30 centimetres.

Add together 36, 12 and 30 to get the perimeter, which is 78 centimetres.

Here is a question for you to try.

Pause the video to complete the task and restart when you are finished.

Here is the answer.

As we're told that there are 36 children on the train.

We can work out that each part is worth 18 people.

So that must be 18 times five adults on the train.

That's 90 adults, 10% of adults get off the train.

10% of 90 is nine.

So when nine adults get off, there will be 81 adults left on the train.

Here is a final question for you to try.

Pause the video to complete the task and restart when you are finished.

Here are the answers.

We're given the information that the width is 10.

5.

In the ratio, the width is represented by three parts.

So divide 10.

5 by three, to get 3.

5 centimetres in each part.

To find the length.

Multiply 3.

5 centimetres by five, giving us 17.

5 centimetres for the length.

For part B, we need to find the perimeter first.

The length is 17.

5 and the width is 10.

5.

Add together two lots of 17.

5 and two lots of 10.

5 to get the perimeter, which is 56 centimetres.

The width is 10.

5.

So we simplify 10.

5 to 56.

We always write ratios as integers.

So I doubled each part of the ratio first to get 21:112.

And then I found the highest common factor of these two numbers, which is seven.

Divide both parts by seven to get 3:16.

That's all for this lesson.

I hope you've enjoyed using bar model, the ratio.

Remember to take the exit quiz before you leave.

Thank you for watching.