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.
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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.
