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Surface Area:  The total area of the 2-dimensional surfaces that make up a 3-dimensional object.
 For example, if you peel an orange, the peelings might represent the surface area of the orange. What is left might represent the "volume" of the orange. Another example would be if we look at a fish tank full of water - the surface area would be the sum of the areas of the sides, the bottom, and the top of the tank. The volume would be the amount of water in the tank.In the example to the left, each face of the prism is a rectangle. The area of a rectangle is length x width. Also, there are three faces not seen in the figure (bottom, left and rear faces). Each unseen face is equivalent to one of the visible faces. The area of the front and rear faces is 3 dm x 4 dm = 12 square dm (note: sq. = square and dm = decimeter) each. The area of each side face is 3 dm x 5 dm = 15 sq. dm . The area of the top and bottom faces is 4 dm x 5 dm = 20 sq. dm each. The surface area = area of front face + area of rear face + area of one side face + area of other side face + area of top face + area of bottom face = 12 sq dm + 12 sq dm + 15 sq dm + 15 sq dm + 20 sq dm + 20 sq dm = 94 sq dm. Surface area is used when someone needs to determine how much paint is needed to paint a room of a house or how much wrapping paper is needed to wrap a birthday present.