Art of Problem Solving

2025 AMC 10A Problems/Problem 20: Difference between revisions

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A silo (right circular cylinder) with diameter 20 meters stands in a field. MacDonald is located 20 meters west and 15 meters south of the center of the silo. McGregor is located 20 meters east and <imath>g > 0</imath> meters south of the center of the silo. The light of sight between MacDonald and McGregor is tangent to the silo. The value of g can be written as <imath>\frac{a\sqrt{b}-c}{d}</imath>, where <imath>a,b,c,</imath> and <imath>d</imath> are positive integers, <imath>b</imath> is not divisible by the square of any prime, and <imath>d</imath> is relatively prime to the greatest common divisor of <imath>a</imath> and <imath>c</imath>. What is <imath>a+b+c+d</imath>?


<imath>\textbf{(A) } 118 \qquad\textbf{(B) } 119 \qquad\textbf{(C) } 120 \qquad\textbf{(D) } 121 \qquad\textbf{(E) } 122</imath>
=Solution 1=

Revision as of 14:50, 6 November 2025

A silo (right circular cylinder) with diameter 20 meters stands in a field. MacDonald is located 20 meters west and 15 meters south of the center of the silo. McGregor is located 20 meters east and $g > 0$ meters south of the center of the silo. The light of sight between MacDonald and McGregor is tangent to the silo. The value of g can be written as $\frac{a\sqrt{b}-c}{d}$, where $a,b,c,$ and $d$ are positive integers, $b$ is not divisible by the square of any prime, and $d$ is relatively prime to the greatest common divisor of $a$ and $c$. What is $a+b+c+d$?

$\textbf{(A) } 118 \qquad\textbf{(B) } 119 \qquad\textbf{(C) } 120 \qquad\textbf{(D) } 121 \qquad\textbf{(E) } 122$

Solution 1