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2012 AMC 10B Problem 16

Problem 16 of 25IntermediateGeometry

Three circles with radius 22 are mutually tangent. What is the total area of the circles and the region bounded by them, as shown in the figure?

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Solution

Connect the centers of the three circles. This forms an equilateral triangle of side 44, with area 434\sqrt3. The included part of each circle is a 300300^\circ sector, whose area is 300360π22=10π3\dfrac{300}{360}\pi\cdot2^2=\dfrac{10\pi}{3}. The total area is 310π3+43=10π+433\cdot\dfrac{10\pi}{3}+4\sqrt3=10\pi+4\sqrt3. Thus, A is the correct answer.

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Concepts: tangent circles · sector · equilateral triangle · area decomposition

Problem text and solution from the LIVE past-contest archive. See also the AoPS wiki page for community solutions.