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AMC 12 2017a Problem 25

  • Paper

The vertices VV of a centrally symmetric hexagon in the complex plane are given by V={2i,−2i,18(1+i),18(−1+i),18(1−i),18(−1−i)}.V=\left\{ \sqrt{2}i,-\sqrt{2}i, \frac{1}{\sqrt{8}}(1+i),\frac{1}{\sqrt{8}}(-1+i),\frac{1}{\sqrt{8}}(1-i),\frac{1}{\sqrt{8}}(-1-i) \right\}. For each jj, 1≤j≤121\leq j\leq 12, an element zjz_j is chosen from VV at random, independently of the other choices. Let P=∏j=112zjP={\prod}_{j=1}^{12}z_j be the product of the 1212 numbers selected. What is the probability that P=−1P=-1?

(A) 5⋅11310(B) 52⋅112⋅310(C) 5⋅1139(D) 5⋅7⋅112⋅310(E) 22⋅5⋅11310\textbf{(A) } \dfrac{5\cdot11}{3^{10}} \textbf{(B) } \dfrac{5^2\cdot11}{2\cdot3^{10}} \textbf{(C) } \dfrac{5\cdot11}{3^{9}} \textbf{(D) } \dfrac{5\cdot7\cdot11}{2\cdot3^{10}} \textbf{(E) } \dfrac{2^2\cdot5\cdot11}{3^{10}}

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

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