This is a most unusual paragraph. How quickly can you find out what is so unusual about it? It looks so ordinary you’d think nothing was wrong with it – and in fact, nothing is wrong with it. It is unusual though. Why? Study it, think about it, and you may find out. Try to do it without coaching. If you work at it for a bit it will dawn on you. So jump to it and try your skill at figuring it out. Good luck! Don’t blow your cool!
A key. It has a jagged cut in order to fit the lock. A locked door keeps people out and the keyhole is dark. Key rings are a common way to hold a set of keys, and when you’re using a key that one is quiet, but the rest jingle and jangle.
You’re waiting to board your flight at the airport with 99 other passengers, each with an assigned seat. All but one of the passengers will gladly sit in their designated seat. The only exception is Randall, a scoundrel who refuses to follow the rules. When he boards, he will choose a random, unoccupied seat.
If a rule-following passenger finds someone in their spot, they will choose another one at a random from the remaining unoccupied seats.
What is the probability that the last person to board the plane will sit in their proper seat?
The randomness stops as soon as someone else sits in Randall’s assigned seat. The chances of this happening range from 1 out of 99 to 1 out of 1 (when only one seat remains).
Thus, the probability of the last person sitting in their own seat can be calculated as 1/99 plus the sum of 2 to 98 of the formula 1 / n × (n + 1), which works out to 0.5, or 50%.
So there’s a 50% chance the last passenger will sit in their own seat thanks to Randall for screwing up order and procedure when boarding an aircraft.