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2021 Individual #24

On a circle OO with radius OA\overline{OA}, points BB and CC are drawn such that AOC=BOA=30\angle AOC = \angle BOA = 30^\circ, as shown. A second circle passing through BB, CC, and the midpoint of OA\overline{OA} is drawn. The ratio of the radius of this new circle to the radius of circle OO can be expressed in the form a3bc\tfrac{a \sqrt 3 - b}{c} where aa, bb, and cc are positive integers and cc is as small as possible. What is a+b+ca + b + c? [asy] size(100); pair O,A,B,C; O = (0,0); label("OO",O,W); A = (2,0); label("AA",A,E); B = (sqrt(3),1); label("BB",B,N*1.8); C = (sqrt(3),-1); label("CC",C,S*1.8); draw(Circle(O,2)); dot((1,0)^^A^^B^^C^^O); draw(O--B); draw(O--C); draw(O--A); draw(Circle((2.04904,0),1.04904),dashed); [/asy] Note: In the diagram, AA is not necessarily the center of the second circle.
<spanclass=latexbold>(A)</span>10<spanclass=latexbold>(B)</span>12<spanclass=latexbold>(C)</span>15<spanclass=latexbold>(D)</span>21<spanclass=latexbold>(E)</span>27<span class='latex-bold'>(A) </span>10\qquad<span class='latex-bold'>(B) </span>12\qquad<span class='latex-bold'>(C) </span>15\qquad<span class='latex-bold'>(D) </span>21\qquad<span class='latex-bold'>(E) </span>27