Final answer:
Proportions are statements of equivalent values of different units in terms of ratios, like 1/2 = 3/6. Unit rates and unit scales are types of ratios used in measurements and scaling which relate different units or dimensions. For example, a unit rate could be 55 miles per hour and a unit scale could be 1 inch = 100 feet.
Step-by-step explanation:
The correct answer to the question is a) Proportions. Proportions are statements of equivalent values of different units in the form of ratios. An example of a proportion is 1/2 = 3/6, where both ratios represent the same value. A unit rate, such as 55 miles per hour (55/1 miles/hour), is a type of ratio where one of the measurements has a value of 1.
Similarly, a unit scale is a ratio that compares the dimensions of an actual object to a scale representation. For example, a unit scale on a map might be expressed as 1 inch = 100 feet, written as a ratio of 1 inch/100 ft.
In the metric system, which is part of the system of measurement commonly used worldwide, proportions play a crucial role as conversion factors when dealing with different units. A conversion factor is a fraction with equivalent quantities in the numerator and the denominator, but expressed in different units, essentially symbolizing a ratio of 1 even when non-unity numeric values are used.