Manhattan Prep
A regular octagon (a polygon with 8 sides of identical length and 8 identical interior angles) is constructed. Next, an equilateral triangle (with sides identical in length to those of the octagon) is attached to each side of the octagon, such that each side of the octagon coincides exactly with the side of the triangle. Finally, each triangle is folded over that coincident side onto the octagon, covering part of the latter's area. Approximately what proportion of the area of the octagon is left uncovered?
A. 60%
B. 50%
C. 40%
D. 30%
E. 20%
OA D