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073概率中等derivationmedium

Divisibility Events and the Containment Trap

题目

Let Ω={0,1,2,,11}\Omega = \{0, 1, 2, \ldots, 11\} with uniform probability P({k})=1/12P(\{k\}) = 1/12 for each kk. Define three events based on divisibility: A={kΩ:2k}A = \{k \in \Omega : 2 \mid k\} (even numbers), B={kΩ:3k}B = \{k \in \Omega : 3 \mid k\} (multiples of 33), C={kΩ:4k}C = \{k \in \Omega : 4 \mid k\} (multiples of 44). (a) List each event explicitly and compute P(A)P(A), P(B)P(B), P(C)P(C). (b) For each of the three pairs (A,B)(A,B), (A,C)(A,C), (B,C)(B,C), determine whether the pair is independent by computing P(intersection)P(\text{intersection}) and comparing with the product of marginals. (c) Identify which pair fails independence and explain the structural reason.

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