### Let’s Think About It

Josh is building a scale diagram of Mount Everest. He knows that Mount Everest is 29,035 feet high. He doesn’t want his model to be too large so thinks he should use . If Josh uses this scale, will his model be too big?

In this concept, you will learn to use unit scale when problem solving.

### Guidance

Sometimes in life, you have a real-life object that you want to represent in a smaller form. Think about buildings. When an architect is planning a building design, he or she may design a model of the building. This model shows the dimensions of the building in a smaller way. When you do this, you take the actual dimensions and shrink them down to build a model. When you do this, you create a **unit scale** for the model. When you create a unit scale, you decide on an appropriate measurement to represent an actual measurement.

First, let’s look at a unit scale.

This is a unit scale. You have a unit represented by the one inch. Remember that when you talk about unit, you are talking about a relationship to one. You have one inch represented by three feet.

The one inch is the scale dimension and the three feet is the actual dimension we are measuring.

Now, not all objects that you will create a model of will measure exactly what the unit scale does, so you have to use a unit scale to show the relationship between **scale dimensions** and **actual dimensions**. **Scale dimensions** are the dimensions of the model, and **actual dimensions** are the real–life dimensions.

Let’s look at an example.

Using the unit scale above, what would be the relationship between the scale dimensions and the actual dimensions for an object 24 feet long?

First, let’s think about your unit scale.

Next, use the unit scale to write a proportion of the scale dimensions to the actual dimensions.

Then, cross multiply.

Then, divide both sides by 3 to solve for

.

The answer is 8.

Therefore,

.If you know the scale dimensions and the unit scale, then you can find the actual dimensions with the unit scale.

If you know the actual dimensions and the unit scale, then you can find the scale dimensions with the unit scale.

Let’s look at an example.

What is the scale length of the object if the unit scale is 2 inches : 4 feet and the actual dimensions of the object is 20 feet?

First, let’s think about your scale.

Next, use the scale dimensions to write a proportion of the scale dimensions to the actual dimensions.

Then, cross multiply.

Then, divide both sides by 4 to solve for

. The answer is 10.Therefore,

.### Guided Practice

Using a unit scale of 1 inch : 8 feet, what is the actual dimension of an object with a scale dimension for length of 5 inches?

First, let’s think about your unit scale.

Next, use the unit scale to write a proportion of the scale dimensions to the actual dimensions.

Then, cross multiply.

The answer is 40.

Therefore, the actual dimensions are

.### Examples

#### Example 1

Using a unit scale of 1 inch : 5 feet, what is the actual dimension of an object with a scale dimension for length of 25 feet?

First, let’s think about your unit scale.

Next, use the unit scale to write a proportion of the scale dimensions to the actual dimensions.

Then, cross multiply.

Then, divide both sides by 5 to solve for

.

The answer is 5.

The actual dimensions are

.#### Example 2

Using a unit scale of 1 inch : 5 feet, what is the actual dimension of an object with a scale dimension for length of 3 inches?

First, let’s think about your unit scale.

Next, use the unit scale to write a proportion of the scale dimensions to the actual dimensions.

Then, cross multiply.

The answer is 15.

The actual dimensions are

.#### Example 3

Using a unit scale of 1 inch : 5 feet, what is the actual dimension of an object with a scale dimension for length of 75 feet?

First, let’s think about your unit scale.

Next, use the unit scale to write a proportion of the scale dimensions to the actual dimensions.

Then, cross multiply.

Then, divide both sides by 5 to solve for

.

The answer is 15.

The actual dimensions are

.### Follow Up

Remember Josh’s mountainous model?

Josh is using scale dimensions of . Mount Everest is 29,035 feet.

First, let’s think about your unit scale.

Next, use the unit scale to write a proportion of the scale dimensions to the actual dimensions.

Then, cross multiply.

Then, divide both sides by 2000 to solve for

.

The answer is 14.5.

Josh’s model of Mount Everest would be 14.5 inches tall.

### Video Review

https://www.youtube.com/watch?v=gHqF4zHBGkU&feature=youtu.be

### Explore More

Find the scale dimension given the scale. Write a proportion and an answer for each problem. There are two answers for each problem.

1. Scale is

, the actual dimension is 18 feet2. Scale is

, the actual dimension is 20 feet3. Scale is

, actual dimension is 10 feet4. Scale is

, actual dimension is 72 feet5. Scale is

, actual dimension is 16 feetUsing a scale of 1 to 2, figure out the actual dimensions given each scale.

6. 4 to

7. 6 to

8. 9 to

9. 12 to

10. 14 to

Using a scale of 3 to 4, figure out the actual dimensions given each scale.

11. 6 to

12. 9 to

13. 12 to

14. 18 to

15. 36 to