2002 AMC 10B Problem 5

Below is the professionally curated solution for Problem 5 of the 2002 AMC 10B, from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2002 AMC 10B solutions, or check the answer key.

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Concepts:tangent circlescircle area

Difficulty rating: 1020

5.

Circles of radius 22 and 33 are externally tangent and are circumscribed by a third circle, as shown in the figure. What is the area of the shaded region?

3π3\pi

4π4\pi

6π6\pi

9π9\pi

12π12\pi

Solution:

The two small circles line up along a diameter of the big circle, so that diameter is 23+22=102\cdot3 + 2\cdot2 = 10 and the large radius is 5.5.

The shaded region is the large disk with the two small disks removed: π(52)π(32)π(22)=π(2594)=12π.\pi(5^2) - \pi(3^2) - \pi(2^2) = \pi(25 - 9 - 4) = 12\pi.

Thus, the correct answer is E.

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