1. Proportions
Rachel Wraley

2. Properties of Proportions
a c a b
─ = ─ then, ─ = ─
b d c d
a c a+b c+d
─ = ─ then, ── = ──
b d b d

3. Proportion Uses When the length of one side of an object is unknown.
When trying to scale a project (from a blueprint to a building or vice versa)

4. Example #1
A scale model of the Titanic is inches long and inches wide. The real Titanic was feet long. Can you find out how wide the Titanic was?

5. Solution: Step 1 Set up a Proportion: Titanic (unknown) Titanic
Width of Length of
Titanic (unknown) Titanic
────────── = ───────
Width of Length of
Model Model

6. Step 2
Substitute the given values and the unknown variable for the information. Don’t forget labels.
x ft ft
────── = ───────
11.25 in in

7. Step 3 Solve the resulting equation. 11.25 · (882.75)
Multiply each side by 11.25
11.25 · (882.75)
x = ────────── = 92.4 ft
107.5
So the Titanic’s width is 92.4 ft.

8. Exercise Problem
You’ve been given a blueprint to a house. The scale is 1/8 inch is equal to 1 foot.
If the blue dimensions are length: 81 ft
width: 62 ft.
What would the blueprint’s scale dimensions be?

9. How did you do? Did you get 10.125 inches for the length?
How about 7.75 inches for the width?

10. If not, here’s the solution
You divide the actual dimension (81 ft & 62 ft) by the denominator of the scale (8).
── = ── = 7.75

11. Congratulations
You can now solve any proportion problem that comes your way during Operation Hinkle.