A linear model combines a constant rate of change with an initial value. In y = mx + b, m is the change in y per unit of x, while b is the value when x is zero.
Key Rules
Calculate slope as change in y divided by change in x using a consistent point order.
Interpret the intercept in the problem’s units.
Substitute a known point to check a proposed equation.
Common Mistakes to Avoid
Reversing the rise and run.
Treating the starting charge as the per-unit rate.
SAT Strategy Tips
→Label units before calculating a slope.
→A table is linear only when equal input changes produce equal output changes.
Example Question
A taxi charges a starting fee of 4 dollars plus 2 dollars per mile. What is the cost of a 5-mile trip?
Ready to practice?
Apply what you learned with real SAT questions on this topic.