2001 AMC 10 Problem 18
The plane is tiled by congruent squares and congruent pentagons as indicated. The percent of the plane that is enclosed by the pentagons is closest to
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Solution
Consider a repeating block of nine small squares. Four of these nine squares are not part of the pentagons, so the pentagons cover of the area.
This is closest to Thus, the correct answer is D.