What is the mathematical operation used to compare two values?

The mathematical operation used to compare two values is best described as a ratio. A ratio expresses the relative size of two quantities in relation to each other, allowing for a straightforward comparison. For instance, if you have two numbers, say 4 and 2, the ratio of these numbers is 4:2, which can also be simplified to 2:1. This indicates that for every 2 units of one quantity, there is 1 unit of another.

In the other options, proportion deals with the equality of two ratios, and percent is a way to express a number as a fraction of 100, which is a more specific application of fractions. A fraction represents a part of a whole but does not itself provide a direct comparison like a ratio does. Thus, among the choices given, ratio is the most suitable term for the operation of comparing two values directly.