Multimedia Gallery - The following example illustrates a misconception when determining the perimeter of a 2-D shape.

a rectangle whose perperimeter is surrounded with 18 square tiles.

January 31, 2012

The following example illustrates a misconception when determining the perimeter of a 2-D shape.

The following example illustrates a misconception when determining the perimeter of a 2-D shape: A student is asked to find the perimeter (the length of the continuous line forming the boundary of a closed geometric figure) of this 2-D rectangle. The student is told that the perimeter of the rectangle can be found by surrounding the rectangle with square tiles, including tiles at each of the four corners. The student claims that the perimeter of the rectangle is 22 tiles. However, the actual perimeter is 18 tiles. The student is not distinguishing the edges of the tiles as length units from the square tiles that are area units--the ability to visualize the difference is crucial in understanding what one is measuring.

Credit: Courtesy of Jack Smith, MSU

Images credited to the National Science Foundation, a federal agency, are in the public domain. The images were created by employees of the United States Government as part of their official duties or prepared by contractors as "works for hire" for NSF. You may freely use NSF-credited images and, at your discretion, credit NSF with a "Courtesy: National Science Foundation" notation.

Additional information about general usage can be found in Conditions.

Also Available:
Download the high-resolution JPG version of the image. (29 KB)

Use your mouse to right-click (Mac users may need to Ctrl-click) the link above and choose the option that will save the file or target to your computer.