Pregunta de entrevista

Entrevista de Strategist

-New York, NY

Goldman Sachs

10 people of different ages sitting around a table. What's the probability of sitting in an age-ascending order?


Respuestas de entrevistas

3 respuestas


Another way to think about it: You have (n-1)! different arrangement to sit people around the table. You fix one person, and sit the rest. Or you take an arrangement and divide that by n "rotations". Both ways work. The ascending order is just 1 order fixed. 2 if you count both ways.

Anónimo en


Both of the above answers are correct 20/10! = 2/9!, and when n = 10, we have 2/(10-1)! = 2/9!. The key is the reasoning described in the second comment. Indeed, fix one person and sit the rest 9 people. Let's say each people's name is just their age. The only 2 possible orderings of the remaining 9 people such that we have an ascending order around a table would be 1 2 3 4 5 6 7 8 9, and 9 8 7 6 5 4 3 2 1. Thus, of the 9! possibilities, 2 of them are in ascending order.

Kelvin en


The answer is 20/10!. There are 10! ways to sit around the table and 10 ways to sit in ascending order. But since you didn't specify direction, there's actually 20 ways to sit around the table in order.

Chini en

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