Finding the Perimeters of Shapes Made Up of Rectangles and Squares

Some figures are a combination of rectangles and squares. Think of the floor plan of your house. Assuming you don't have any turrets or other non-rectangular areas, it's likely that you could sketch the floor plan using only rectangles and squares. To find the perimeter of such a figure, look only at the outside edges.

   

Example:

Find the cost of weather stripping needed to seal the edges of the boat hatch pictured at right. Weather stripping costs $0.12 per foot.

Recall that perimeter is the sum of all the outside edges:

P = 10 ft + 25 ft + 5 ft + 10 ft + 5 ft + 15 ft = 70 ft

The perimeter of the hatch is 70 feet.

The dimensions highlighted in red were not explicitly stated on the diagram, but enough information was provided to determine these values. Take a moment now to be sure you understand where the additional 10 feet and 5 feet came from.

Finally, calculate the cost of the required weather stripping.

70 ft X ($0.12/ft) = $8.40