[Toolish]

I see and understand the logic you are trying to use, but I think it is wrong.

The fact one door was preselected has NO bearing on which door has the car behind it.

If you walk into a room with 3 doors, 1 is open showing a goat, and the other 2 are closed, you then have to pick a door knowing a car is behind 1, what is your chance of picking the car?

I say 50%...

This is exactly the same scenario, the fact that there was a previous action and door reveal does not change the probabilites related the this event...like I said look up Mutually exclusive...

It is like a coin toss, if you toss a coin and get a head 5 times in a row there is still a 50% chance the next will be a head, the previous events don't change the probabilities involved in this event.