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AMC 12 2023a Problem 24

  • Paper

Let KK be the number of sequences A1A_1, A2A_2, …\dots, AnA_n such that nn is a positive integer less than or equal to 1010, each AiA_i is a subset of {1,2,3,…,10}\{1, 2, 3, \dots, 10\}, and Ai−1A_{i-1} is a subset of AiA_i for each ii between 22 and nn, inclusive. For example, {}\{\}, {5,7}\{5, 7\}, {2,5,7}\{2, 5, 7\}, {2,5,7}\{2, 5, 7\}, {2,5,6,7,9}\{2, 5, 6, 7, 9\} is one such sequence, with n=5n = 5.What is the remainder when KK is divided by 1010?

(A) 1(B) 3(C) 5(D) 7(E) 9\textbf{(A) } 1 \textbf{(B) } 3 \textbf{(C) } 5 \textbf{(D) } 7 \textbf{(E) } 9

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

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