A proportion is an equation which states that two ratios are equal.
For example, [tex]\frac{a}{b} = \frac{c}{d}[/tex] is an example of a proportion. In the given proportion, a and d are called extremes and b and c are called means. The first property that I will talk about states that the product of the extremes equals the product of the means. This idea is called the (means-extreme property).
