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
. Fix the youngest person's seat; the other six are then in one of equally likely orders. Exactly two of these (ages increasing clockwise or anticlockwise) qualify, so the probability is .
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Open the worked solutionLessons behind this question
- Counting and Combinatorics
- Sample Spaces, Events, and the Probability Axioms
- Conditional Probability, Total Probability, and Bayes' Rule
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