1. Scale Drawing and Scale Models
7-5
Scale Drawing and Scale Models
Course 3

2. Vocabulary
Scale Drawing - a two-dimensional drawing that accurately represents an object.
Scale - the ratio of the dimensions in the drawing to the dimensions of the actual object.
Scale Model - a three-dimensional model that accurately represents a solid object.

3. 1 unit on the drawing is 20 units.
Scale
Interpretation
1:20
1 unit on the drawing is 20 units.
1 cm:1 m
1 cm on the drawing is 1 m.
in. = 1 ft
in. on the drawing is 1 ft.
1 4
1 4
The scale a:b is read “a to b.” For example, the scale 1 cm:4 m is read “one centimeter to four meters.”
Reading Math

4. Using proportions to find actual lengths on a map:
Video:

6. We can use proportions to find unknown scale.
For example: What is the scale of a drawing in which a 9 ft wall is 6 cm long?
Set up a proportion and solve.
Write the proportion as model to actual:
6cm/9ft = 1cm/xft
The scale is 1 cm: 1.5 ft.
(The model length is usually simplified
to a measure of 1 to find the scale)

7. We can use proportions to find unknown lengths:
A. The length of an object on a scale drawing is 2 cm, and its actual length is 8 m. The scale is 1 cm: __ m.
1 cm
x m
2 cm
8 m =
Set up the proportion using
model length .
actual length
Solve the proportion. (Multiply the cross product you know and divide by the third value.
The scale is 1 cm:4 m.

8. Here is another example:
The length of an object on a scale drawing is 4 cm, and its actual length is 12 m. The scale is 1 cm: __ m.
1 cm
x m
4 cm
12 m =
Set up proportion using
model length .
actual length
Solve the proportion.
The scale is 1 cm:3 m.

9. Here is an example finding unknown length:
Use 0.25 in = 1 ft scale, how long would a drawing of a 22 ft car be?
Set up proportion using
model length .
actual length
Solve the proportion.
The scale drawing of the car would be 5.5 in long.

10. Your turn: Finding Unknown Dimensions Given Scale Factors
A model of a 27 ft tall house was made using a scale of 2 in:3 ft. What is the height of the model?
Set up a proportion and solve
The height of the model is 18 in.

11. Let’s put an example in our notes

12. You Try: Example 3
A model of a 24 ft tall bridge was made using a scale of 4 in.:2 ft. What is the height of the model?
Set up a proportion and solve.
The height of the model is 48 in.

13. You Try: Example 3
The height of a person on a scale drawing is 4.5 in. The scale is 1:16. What is the actual height of the person?
Set up a proportion and solve.
The height of the person is 72 in.