A “Friend” in Need

Each year in my mathematics classes, when we came to the section on perimeters of plane figu res, I fou nd misunderstandings. Although most of my students had been introduced to the concept of perimeter, many of them had misconceptions about it. The most common confusion seemed to come from the fact that they had been well drilled in finding area and by habit, especially in the case of quadrilaterals, automatically wanted to multiply length by width. The second most common error may also have stemmed from a confusion with area. In this case they would add one length to one width, thereby producing a semi-perimeter or in cases of figures with many sides, a very short pan of the distance a round the figure. The third error was the mislabeling of the units in the answers as square units or cubic units, or of not labeling them at all.