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Seven people around a table sorted by age

Question

Seven people, all of different ages, take the seven seats at a round table in a uniformly random arrangement. What is the probability that going around the table, in one direction or the other, their ages increase steadily from the youngest to the oldest?

Short answer

1360\tfrac1{360}. Fix the youngest person's seat; the other six are then in one of 6!=7206!=720 equally likely orders. Exactly two of these (ages increasing clockwise or anticlockwise) qualify, so the probability is 2720=1360\tfrac{2}{720}=\tfrac1{360}.

Adapted from QuantQuestions.io; question and answer rewritten by SelfMadeQuant.com.

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