Randomly Assigned Meetings Across Rooms (Balls-in-Bins)
Setup
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There are N rooms and k meetings.
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Each meeting independently chooses a room uniformly at random (multiple meetings can be in the same room).
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Let X₁ be the number of meetings assigned to Room 1.
Question
Given that Room 1 is non-empty (i.e., X₁ ≥ 1), what is the expected number of meetings in Room 1, E[X₁ | X₁ ≥ 1]?
Hint: Use conditional probability and linearity of expectation.