Can be used to solve problems with ratios.

Problem: The shadow of a flagpole is 70 ft and the shadow of your mom is 10 ft. If your mom is 5 ft 3 inches, how tall is the flag pole?

Ratio shadow length: height

- your mom → 10 ft : 5.25 ft
- flagpole → 70 ft : x ft

Change ratios in proportions

* cross multiplication

Scale room problem: A scale drawing is made with the length of the room as 12 cm and width as 7 cm. If the actual length of the room is 30 ft, then what is the actual width?

* cross multiplication