EDIT: I lied. I have no idea about the probability.
I just did it this year. Think!
The chance of selecting one person and them being mafia is 21%. Out of 12 people, the likeliness is 100% due to there being 3 mafia.
Oh, fuck, I can't remember.
Kimi wa ne tashika ni ano toki watashi no soba ni ita
Itsudatte itsudatte itsudatte
Sugu yoko de waratteita
Nakushitemo torimodosu kimi wo
I will never leave you