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
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