# Variable

A **variable** in statistics refers to a measurement whose value can **vary**. For example, the variable "speed" (e.g., of a car) can vary between 0 and the maximum speed of the car.

A variable differs from a constant, which is a fixed value.

## Contents

## More[edit]

For people used to basic math, it may be confusing to think of a math problem that starts with `1 + a`

, but in algebra such combinations are common.

*a* stands for a number we don't know. It could be 1, 5, 7, ¾: any number you can imagine. What we call *a* is a variable, because unlike normal, or *constant*, numbers, it may vary.

A variable can be any letter. *t* is seldom used as a variable because it can get mixed up with +, but *x* is a commonly used variable. It doesn't get confused with X, the sign for multiplication, because in algebra X is not used for that purpose: * or parentheses are used instead. (`2*4`

and `2(4)`

mean the same thing as `2 X 4`

.)

## How is it used?[edit]

Variables are used as placeholders in problems; they stand for unknown numbers. It may be easy to figure out what the variable stands for; it may be difficult; it may be impossible.

In the problem `a + b = c`

, *c* could be any number which can be made by combining two other numbers. *c* could be 3, as `1 + 2 = 3`

. *c* could be 72, as `3 + 69 = 72`

. Where a problem gives more information, the number of solutions becomes more limited. In the problems `1 + 2 = c`

and `c - 2 = 1`

, there are limited values that could be true of *c*.

Figuring out the variable can be as simple as doing the basic math. With the problem `1 + 2 = c`

, we simply add 1 and 2 to figure out that the variable, *c*, equals 3. It can become considerably more complex. Sometimes, a solution is not possible, and the goal is to *simplify* or *reduce* the problem as far as it can be simplified. We cannot figure out what *c* is in the problem `a + 4 - 2 + 6 = c`

, but we can simplify it into `a + 8 = c`

.

### Exercises[edit]

*For more information, see Solving equations.*

Here are a few simple problems to help you get used to the idea.

**Find the value of the variable.**

- 1 + 3 =
*e* - 3 + 9 =
*x* - 10 - 4 =
*a* - 4 * 2 =
*y* - 10(2) =
*k* - 7 + 11 =
*l* - 5(a) = 15