2012 AMC 10B Problem 16

Below is the professionally curated solution for Problem 16 of the 2012 AMC 10B, from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2012 AMC 10B solutions, or check the answer key.

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Concepts:tangent circlessectorequilateral trianglearea decomposition

Difficulty rating: 1630

16.

Three circles with radius 2 are mutually tangent. What is the total area of the circles and the region bounded by them, as shown in the figure?

10π+43 10\pi+4\sqrt{3}

13π3 13\pi-\sqrt{3}

12π+3 12\pi+\sqrt{3}

10π+9 10\pi+9

13π 13\pi

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.

Problem 16 in Other Years