Variables are the symbols (usually a letter such as x or y) used in algebraic equations that represent an unknown number—and on whose value a function, polynomial, and so on, depends. Variables remain unknown until the equation is solved; thus, they are sometimes referred to as unknowns in an algebraic equation.

You can use algebra to solve word problems by converting known and unknown data into figures and variables. For instance, a word problem might involve two trains, one going 120 mph and one traveling at 112 mph. If the first train is 250 miles from a destination and the second train is 220 miles from the same destination, which train will arrive first?

It is not always easy to work with variables, as there are so many letters used throughout various equations. But in many mathematical and scientific texts, there are some variables that are customary to use. They are listed as follows:

n indicates natural numbers or integers

x represents real numbers

z stands for complex numbers.