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Explanation:
If you used scissors to cut a vertical slice down the lampshade, then it can be unrolled to form a rectangle.
The horizontal portion of this rectangle is the distance around the circle, which is the perimeter of the circle, or the circumference. That's C = 2pi*r. Check out the diagram below to see what I mean.
The diagram shows that the diameter is 20 cm, so the radius is half that at 20/2 = 10 cm.
The circumference is C = 2*pi*r = 2*pi*10 = 20pi cm exactly
The height of the rectangle is the height of the cylinder, which is h = 30 as shown in the diagram.
The area of the rectangle is length*height = (20pi)*(30) = 600pi square cm exactly.
If we were to use something like pi = 3.14, then its approximate area is 600*pi = 600*3.14 = 1884 square cm
Let's bump this up by 10%. To do so, we'll multiply by 1.10
1.10*1884 = 2072.4
