Can you think of a rule that uses a letter or a variable number? What about the formula for the area of a rectangle? A stands for area, L stands for length, and W stands for the width. So, depending on the size of the rectangle, L and W could be any number. It’s a variable.

When you’re using letters in the place of numbers, they’re also called pronumerals. That’s how we’ll start off using them. We’ll call them pronumerals for now. The word pronumeral is made up of two parts. You’re already familiar with the word numeral. The pro at the beginning means on behalf of or in the place of. So, a pronumeral is something used in the place of a numeral.

The most common pronumerals are letters of the alphabet like, A, B, C, X, Y, and so on. Here are some examples of algebraic expressions: X + Z, 2A – AB, Y – 3, M2 / 7. These expressions don’t tell us very much. We can’t work out an answer for them unless we know the value of the pronumerals. For example, if we knew that Y equaled 5, we could work out this example simply be substituting 5 in the place of Y. So, if Y is 5, 5 minus 3 is 2, of course.