The area and perimeter trap
A free TEAS® math explainer with an original practice question
Perimeter is the distance around a shape. Area is the space it covers. For a rectangle, perimeter is 2 × (length + width) and area is length × width.
The wording tells you which one you need. Fencing, trim, a border or walking around the edge means perimeter, in plain units such as meters. Carpet, paint, tiles or covering a surface means area, in square units such as m².
A second trap is adding only one length and one width. A rectangle has two of each, so add all four sides.
Try a sample question
A rectangular dog run is 13 m long and 6 m wide. How many meters of fencing are needed to surround the entire run?
- A.19 m
- B.26 m
- C.38 m
- D.78 m
Show the answer
C. 38 m
38 m is correct. Add both lengths and both widths: 13 + 13 + 6 + 6. Multiplying 13 by 6 gives area, but fencing follows the boundary.
Why the other answers tempt:
- A. 19 m counts one length and one width, leaving out the other two sides.
- B. 26 m counts both long sides but leaves out both short sides.
- D. 78 is the area in square meters; fencing measures the boundary in meters.
Perimeter surrounds; area covers.
Checked against OpenStax Prealgebra 2e, 9.4 Use Properties of Rectangles, Triangles, and Trapezoids. Original question, not from a real test.
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