olymmath

AMC 12 2025a Problem 12

  • Paper

The ''harmonic mean'' of a collection of numbers is the reciprocal of the arithmetic mean of the reciprocals of the numbers in the collection. For example, the harmonic mean of 4,4,4,4, and 55 is

113(14+14+15)=307.\frac{1}{\frac{1}{3}(\frac{1}{4}+\frac{1}{4}+\frac{1}{5})}=\frac{30}{7}.

What is the harmonic mean of all the real roots of the 40504050th degree polynomial

∏k=12025(kx2−4x−3)=(x2−4x−3)(2x2−4x−3)(3x2−4x−3)...(2025x2−4x−3)?\prod_{k=1}^{2025} (kx^2-4x-3)=(x^2-4x-3)(2x^2-4x-3)(3x^2-4x-3)...(2025x^2-4x-3)?

\textbf{(A)}-\frac{5}{3} \textbf{(B)}-\frac{3}{2} \textbf{(C)}-\frac{6}{5} \textbf{(D)}-\frac{5}{6} \textbf{(E)}~-\frac{2}{3}

Dataset text AMC 12 2000 to 2025. Quoted with source.

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B

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