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Problem 184: (2021 Fall AMC 10a, 19)
A disk of radius $1$ rolls all the way around the inside of a square of side length $s>4$ and sweeps out a region of area $A$. A second disk of radius $1$ rolls all the way around the outside of the same square and sweeps out a region of area $2A$. The value of $s$ can be written as $a+\frac{b\pi}{c}$, where $a,b$, and $c$ are positive integers and $b$ and $c$ are relatively prime. What is $a+b+c$? $\textbf{(A)} ~10\qquad$ $\textbf{(B)} ~11\qquad$ $\textbf{(C)} ~12\qquad$ $\textbf{(D)} ~13\qquad$ $\textbf{(E)} ~14$
Solution
Exercise 184: Solution
A disk of radius $2$ rolls all the way around the inside of a square of side length $s>8$ and sweeps out a region of area $A$. A second disk of radius $2$ rolls all the way around the outside of the same square and sweeps out a region of area $\frac32A$. The value of $s$ can be written as $a+\frac{b\pi}{c}$, where $a,b$, and $c$ are positive integers and $b$ and $c$ are relatively prime. What is $a+b+c$?
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