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number theory intermediate
Problem
As shown below, convex pentagon has sides , , , , and . The pentagon is originally positioned in the plane with vertex at the origin and vertex on the positive -axis. The pentagon is then rolled clockwise to the right along the -axis. Which side will touch the point on the -axis? 
(A)
(B)
(C)
(D)
Solution
The perimeter of the polygon is . Hence as we roll the polygon to the right, every units the side will be the bottom side. We have . Thus at some point in time we will get the situation when and is the bottom side. Obviously, at this moment . After that, the polygon rotates around until point hits the axis at . And finally, the polygon rotates around until point hits the axis at . At this point the side touches the point . So the answer is
Final answer
C