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Expression evaluation is like following a set of instructions to solve a puzzle. It refers to the process of calculating the value of a mathematical expression. In expressions, numbers, variables, and operations, such as addition or subtraction, are combined. To evaluate an expression, you follow mathematical rules to arrive at a single value.
When evaluating expressions with variables, substituting each variable with its actual value is crucial. This substitution transforms the abstract expression into a solvable calculation.
For example, let's take the simple expression \(a - c\). To begin the evaluation, replace any variables with their known values, and then carry out the arithmetic operations. Substituting given numbers into the expression makes it much easier to solve.

Variable substitution is an essential technique in prealgebra. It involves replacing variables with their given values to simplify and evaluate an expression. Consider variables as placeholders for unknown or specific numbers in mathematical expressions.
When we are given values for the variables, we substitute these values into the expression, replacing each letter with its corresponding number. This changes the expression from abstract to concrete.
For instance, in the expression \(a - c\), if \(a\) is \(-2\) and \(c\) is \(14\), the expression becomes \(-2 - 14\) upon substitution. By transforming the expression this way, we can directly perform arithmetic operations to find the result.

Integer operations are fundamental in prealgebra, encompassing addition, subtraction, multiplication, and division involving whole numbers. These operations follow specific rules, especially when dealing with positive and negative integers.
Key facts about integer operations include:

• Adding two positive integers yields a positive result.
• Adding two negative integers gives a negative result. To add them, find the sum of their absolute values and apply a negative sign.
• Subtracting a positive integer from a negative integer is like adding two negative numbers.
• For \(-2 - 14\), rewrite it as \(-2 + (-14)\). This method ensures consistent handling of signs.

Integer operation rules help maintain accuracy in calculations, making them a cornerstone of prealgebra success.