Final answer:
A proportion expresses the equality of two ratios, such as 1/2 = 3/6. It can take various forms, including unit rates like 55 miles per hour or unit scales in measurements, and is used across many disciplines from science to map reading.
Step-by-step explanation:
A proportion is indeed a method of expressing equality between two ratios. For example, 1/2 = 3/6 is a valid proportion because both ratios represent the same relationship between numbers. Ratios can be used to compare different quantities, like moles of reactants to moles of products in a chemical reaction, or they can represent scale such as on a map where 1 inch could equal 100 feet. In this case the unit scale of a map is a type of ratio comparing a drawing or model's dimensions to that of the actual object it represents, like 0.5 inch/100 feet.
When one ratio in a proportion has a value of 1, as in the speed of 55 miles per hour (55/1 miles per hour), this is known as a unit rate. Unlike a unit rate, both values in a unit scale do not have to equal 1. This concept is crucial in various applications including science, health sciences and measurements in both the metric and the customary systems.