Definition: A variable is a letter or symbol that stands for a number that can change or is not yet known.
What is a variable?
A variable is a placeholder, usually a letter such as n, x, or t. It lets you describe a rule for any number instead of one specific number.
How do you use variables?
Mathbot walks 4 blocks every minute. Let m be the number of minutes. Then the distance in blocks is 4m. If m is 3, the distance is 12 blocks. If m is 10, the distance is 40 blocks. The same expression handles every case.
What is the difference between unknown and changing?
In an equation like x + 9 = 15, the variable stands for one hidden number, 6. In a formula like A = lw, the letters l and w can take many values. Both uses are valid.
What are the conventions?
Writing 4m means 4 times m. A letter alone, like m, has a coefficient of 1. You may choose any letter, but picking one that hints at its meaning, like t for time, helps.
What is a common mistake?
Thinking a variable always equals a specific letter-number code. The letter has no built-in value, so x can be any number the problem allows.