Proportional Ratios

Two ratios are proportional if they represent the same relationship.
-  A proportion means that two ratios are equal. It can be written in two ways:      
-  The proportion can be written as:
 

Examples:
Example 1.  Solve this proportion for . 
Solution:  Use cross multiplication:
Divide both sides by 2 to find : 

Example 2.  If a box contains red and blue balls in ratio of red to blue, how many red balls are there if blue balls are in the box?
Solution: Write a proportion and solve.
Use cross multiplication: 
Divide to find : . There are 27 red balls in the box.

Example 3.  Solve this proportion for . 
Solution: Use cross multiplication: 
Divide to find : 

Example 4.  Solve this proportion for .
Solution: Use cross multiplication: 
Divide to find :