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Problem 162: (2016 AMC 10a, 15)
Seven cookies of radius $1$ inch are cut from a circle of cookie dough, as shown. Neighboring cookies are tangent, and all except the center cookie are tangent to the edge of the dough. The leftover scrap is reshaped to form another cookie of the same thickness. What is the radius in inches of the scrap cookie? $\textbf{(A) } \sqrt{2} \qquad$ $ \textbf{(B) } 1.5 \qquad$ $ \textbf{(C) } \sqrt{\pi} \qquad$ $ \textbf{(D) } \sqrt{2\pi} \qquad$ $ \textbf{(E) } \pi$
Solution
Exercise 162: Solution
Nine cookies are cut from a circle of cookie dough: eight cookies of radius $1$ inch are arranged in a ring, each tangent to its two neighbors in the ring and to the edge of the dough, and a ninth cookie in the center is tangent to all eight ring cookies. The leftover scrap is reshaped to form another cookie of the same thickness. What is the radius of the scrap cookie?
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