# 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.

## More

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?

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

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

Find the value of the variable.

1 1 + 3 = e

 e=

2 3 + 9 = x

 x=

3 10 - 4 = a

 a=

4 4 * 2 = y

 y=

5 10(2) = k

 k=

6 7 + 11 = l

 l=

7 5(a) = 15

 a=