1. Learn to understand ratios and proportions in scale drawings
Learn to understand ratios and proportions in scale drawings. Learn to use ratios and proportions with scale.

2. What are scale drawings? Scale drawings are everywhere!
On Maps
Footprints of houses
Vehicle design
Can you think of any more?

3. Vocabulary
scale drawing
scale factor
scale model
scale

4. A scale drawing is a proportional two-dimensional drawing of an object.
Its dimensions are related to the dimensions of the actual object by a ratio called the scale factor. For example, if a drawing of a building has
a scale factor of , this means that each
dimension of the drawing is of the
corresponding dimension of the actual building. 1 87 1 87

5. Scale factor is the ratio of the length or size of the drawing or model to the length of the corresponding side or part on the actual object.
A scale model is a proportional three- dimensional model of an object.
A scale is the ratio between two sets of measurements. Scales can use the same units or different units. The photograph shows a scale drawing of the model train.

6. Additional Example 1: Finding a Scale Factor
Identify the scale factor.
13.5
108
Width (in.)‏ 18
144
Length (in.)‏
Blueprint
Room
blueprint length
room length 18
144
Write a ratio using one of the
dimensions. = 1 8 =
Simplify.
A scale factor is always the ratio of the model’s dimensions to the actual object’s dimensions.
Caution! 1 8
The scale factor is .

7. Check It Out: Example 1
Identify the scale factor. 3 18
Wing span (in.)‏ 2 12
Length (in.)‏
Blueprint
Model Aircraft
blueprint length
aircraft length 2 12 =
Write a ratio using one of the dimensions. 1 6 =
Simplify.

8. Copy and paste this link to watch the following video

9. Additional Example 2: Using Scale Factors to Find Unknown Lengths
A photograph was enlarged and made into a poster. The poster is 20.5 inches by 36 inches.
The scale factor is . Find the size of the photograph. 5 1
poster
photo 5 1
Think: = 36 l 5 1 =
Write a proportion to find the length l.
5l = 36
Find the cross products.
l = 7.2
Divide.

10. Additional Example 2 Continued
A photograph was enlarged and made into a poster. The poster is 20.5 inches by 36 inches.
The scale factor is . Find the size of the photograph. 5 1
poster
photo 5 1
Think: =
20.5 w 5 1
Write a proportion to find the width w. =
5w = 20.5
Find the cross products.
w = 4.1
Divide.
The photo is 7.2 in. long and 4.1 in. wide.

11. Copy and paste this link to watch the following video

12. Additional Example 3: Measurement Application
On a road map, the distance between Pittsburgh and Philadelphia is 7.5 inches. What is the actual distance between the cities if the map scale is 1.5 inches = 60 miles?
Let d be the actual distance between the cities.
1.5 60
7.5 d =
Write a proportion.
1.5 · d = 60 · 7.5
Find the cross products.
1.5d = 450
Multiply.
1.5d
1.5
450
1.5 =
Divide both sides by 1.5.
d = 300
The distance between the cities is 300 miles.

13. Check It Out: Example 3
On a road map, the distance between Dallas and Houston is 7 inches. What is the actual distance between the cities if the map scale is 1 inch = 50 kilometers?
Let d be the actual distance between the cities. 1 50 7 d =
Write a proportion.
1 · d = 50 · 7
Find the cross products.
1d = 350
Multiply.
d = 350
The distance between the cities is 350 kilometers.

14. For one more video example, copy and paste this link.

15. Lesson Quizzes
Standard Lesson Quiz
Lesson Quiz for Student Response Systems

16. Lesson Quiz: Part I
Identify the scale factor. 1. 8
1,824
Height (in.)‏
Model
Statue of Liberty 1
228 2.
On a scale drawing, a kitchen wall is 6 inches long.
The scale factor is What is the length of the
actual wall? 1 24
144 inches, or 12 feet

17. Lesson Quiz: Part II 3.
On a road map, the distance from Green Bay to
Chicago is 11 cm. What is the actual distance
between the cities if the map scale is 3 cm = 90 km?
330 km

18. Lesson Quiz for Student Response Systems
1. Identify the scale factor.
A C. 10
B D. 20
Fish
Model
Length (cm)
120 12
1 20
1 10

19. Lesson Quiz for Student Response Systems
2. On a scale drawing, the height of a building
is 60 inches. The scale factor is What is
the height of the actual building?
A. 240 in., or 20 ft
B. 300 in., or 25 ft
C. 600 in., or 50 ft
D. 900 in., or 75 ft
1 15

20. Lesson Quiz for Student Response Systems
3. On a road map, the distance from Washington, DC to New York is 15 cm. What is the actual distance between the cities if the map scale is 3 cm = 50 mi?
A. 150 mi
B. 200 mi
C. 250 mi
D. 300 mi