Perimeter and area of polygons

Last time

Before we start: last time, in Circles, sectors and areas of shapes, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.

Carpets, paint and fences

You want to carpet a room, paint a wall, or fence a garden. Carpet and paint need the area: how much surface. A fence needs the perimeter: the distance round the edge. Mixing these up is the classic mistake. Today you find both for every shape in the syllabus.

Rectangles and squares

Perimeter is the total of all the sides. For a rectangle it is two times length plus width. Area is length times width. For twelve by seven: perimeter thirty-eight, area eighty-four. Units: centimetres for perimeter, square centimetres for area.

Working backwards

A rectangle has a width of six, and the width is one twelfth of the perimeter. So the perimeter is six times twelve: seventy-two. Two lengths plus two widths is seventy-two. So length plus width is thirty-six, and the length is thirty-six minus six: thirty. The area would be thirty times six, one eighty. Check: two times thirty-six is seventy-two.