Question 11
A small movie theater has 30 seats; their numbers are indicated on the tickets. The first 21 people who come to a show take 21 seats without paying attention to the seat numbers. Edmond is the 21st person to arrive. But the remaining 9 ticket holders are perfectionists. If any of them finds his or her assigned seat occupied, the person sitting there is evicted; that person then looks for his or her proper seat and evicts the occupier; and so forth. This migration ends with the spectator whose assigned seat is unoccupied. Find the probability, in percentage, that Edmond will not have to change his seat. Enter only the numerical percentage, without the percent sign.