Key Idea: Perimeter

The perimeter is the total distance around a shape, found by adding up all the side lengths.
The word comes from Greek: “peri” = around, “meter” = measure.

General Rule:

Perimeter=Sum of all side lengths

Why this matters for the SAT:

Perimeter problems appear in geometry and word problems. Understanding that perimeter measures the outside boundary helps distinguish it from area, which measures the inside space.