In many introductory courses you will come across characteristics or elements such as rates, outputs, income, etc., measured by numerical values. Some of these will always remain the same, and some will change. The characteristic or element that remains the same is called a constant. For example, the number of donuts in a dozen is always 12. That means the number of donuts in a dozen is a constant.While some of these characteristics or elements remain the same, some of these values can vary (e.g., the price of a dozen donuts can change from $2.50 to $3.00), we call these characteristics or elements variables.Variable is the generic term for any characteristic or element that changes. You should be able to determine which characteristics or elements are constants and which are variables.
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