In my tutoring travels, I notice that some students get confused when they see subscripts, for example \[{x}_{1}\]. As you know, there are only 26 letters in the alphabet. This is almost always enough to represent variables in algebra, but if a formula indicates a pattern, then this is difficult to do using just letters.A subscript is just a way of showing different unknowns using the same letter. \[{x}_{1}\] is a different unknown than \[{x}_{2}\] but the same letter *x* is used – only the subscript has changed. The subscript number just indicates an order and is not used in calculations.So for example, the method for finding the average of a set of numbers is to add up all the numbers, then divide by the number of numbers you just added. To show this in a maths formula:Average = \[\frac{{x}_{1}\hspace{0.33em}{+}\hspace{0.33em}{x}_{2}\hspace{0.33em}{+}\hspace{0.33em}{x}_{3}\hspace{0.33em}{+}\hspace{0.33em}\cdots\hspace{0.33em}{+}\hspace{0.33em}{x}_{n}}{n}\]Here, the pattern is easy to see. Each number in the set of numbers is given a different subscript. Since the subscript starts at 1 and ends in *n*, you can immediately see that there are *n* numbers, which is why the formula shows us dividing by *n*. The symbol “⋯” is called an *ellipsis* and indicates that you just follow the indicated pattern until you get to the last number, \[{x}_{n}\]. For any specific set of numbers, you know what *n* is, but since the formula is to apply for any set of numbers, we need to use the unknown *n*.Sometimes, the subscript is called an *index*. So in more complex formulas, you may see \[{x}_{i}\] to represent any of the unknowns. So we could say that the average is the sum of all \[{x}_{i}\]‘s divided by *n*.