medium   Probability

Familiar Neighbors

A release-checked medium problem for training Expected Value.

Question

There are $2m$ members (where $m$ > 1) seated randomly around a circular table at the Olympic Members Party. All $2m$ people have unique numbered labels $0,1,\dots, 2x-1$, which represent how many people they know, the person with label $i$ knows exactly $i$ of the other $2x-1$ people at the table. These connections are one way, meaning that just because person $B$ knows person $A$, it does not imply person $A$ knows person $B$. Whats the expected proportion of people that know at least one of the people on either side of them.

Practice focus

This Probability problem is tagged Expected Value. State the random variables and conditioning information explicitly, then check the result against boundary cases before opening hints or a solution.

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