Probability of First Selection Across Rounds
Context: There are 1,000 people. Each round, 10 draws are made. Consider a fixed person.
Case 1: Without Replacement Across the Entire Process
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The process is a single random permutation of all 1,000 people.
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People are partitioned into 100 rounds, 10 per round (positions 1–10 → round 1, 11–20 → round 2, …, 991–1000 → round 100).
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Question: What is the expected round index of the person's (only) selection?
Case 2: With Replacement Within and Across Rounds
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Each round consists of 10 independent draws with replacement from the 1,000 people.
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A person is counted as "selected" in a round if they are drawn at least once in that round (multiple hits in the same round still count as one selection for that round).
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Tasks:
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Derive the exact per-round selection probability p for the fixed person.
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Assuming rounds are i.i.d. with success probability p, the number of rounds until first selection is geometric. Compute its expected value.
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Provide a first-order approximation to p.