Final answer:
A variable is an unknown or changeable quantity used in mathematics to represent values that can vary in equations and problems.
Step-by-step explanation:
An unknown or changeable quantity is called a variable. In mathematics, variables are used to represent values that can change or vary in an equation, expression, or problem. They are typically denoted by letters such as x, y, or z, and their values can be determined or substituted to solve for unknown quantities.
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