Functions — Core Skills

The core idea, one worked example, and short practice.

Written and reviewed by the Study Mondo Education TeamLast updated August 21, 2026

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Functions: The Basics

A function is a rule. You put a number in, the rule does something to it, and one number comes out. Think of a vending machine: press the same button and you always get the same snack.

The name $f(x)$ is read f of x. The letter $f$ is the name of the function, $x$ is the number you put in, and $f(x)$ is the number that comes out. It does not mean $f$ times $x$ .

To evaluate a function, wherever you see $x$ , write the input number instead, then do the arithmetic. Multiply before you add.

Many SAT functions look like $f(x) = mx + b$ . The number multiplied by $x$ is the slope, or rate of change. The number standing alone is the y-intercept, or starting value.

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The core idea, one worked example, and short practice.

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Functions — Core Skills is part of the SAT Prep course on Study Mondo, specifically in the SAT Core Skills Track section. You can explore the full course for more related topics and practice resources.