This is the well known Monty Hall problem.
You have more chances of winning by switching doors.
Let A,B,C denote the events "The ferrari is behind A" and so on
Let HA,HB,HC denote the events "The host opens A" and so on
By Baye's formula,
whereas 
!!
You have more chances of winning by switching doors.
Let A,B,C denote the events "The ferrari is behind A" and so on
Let HA,HB,HC denote the events "The host opens A" and so on
By Baye's formula,