At the beginning of the game you pick one of three doors. Behind one of the three goals is the car and behind the other two goats. Therefore, the probability that you contact the gate with the car pick 33.3 percent (one-third). To 66.7 percent (two thirds) You have a gate with a goat chosen.
For simplicity, we assume that you have chosen Gate A and Gate B and C remain.
What happens next, we divide into two cases - even in the event that you have already chosen with gate A gate with the car and even in the event that there is a goat behind door A: