Intuitively, assume many that it does not matter if you do not change the gate or. Finally, behind one of the two gates and a goat behind the other car. The chances of the car should so either way will be fifty percent.

But this answer is wrong: It is always right to change and increasing his chance on the car to 66.7 percent if we - after the moderator has opened a door - switches to the other gate.

Without any complicated "conditional probabilities" or deep Stochastics, this solution will be explained here:
Solution of goat problem