>>Read Devlin's column again. A B and C are used by Devlin as
>>follows. A is the door that the contestant chooses, C is the
>>"wrong" door that Monty opens and B is the other door that
>>"was not opened". You are arguing apples instead of oranges
>>because using Devlin's lingo, door B is never the door
>>opened by Monty.

>Remember in the (2/3) cases when the car is behind door B or
>C
....
> The losing cases come from when the car is behind door A. Here Monty has a choice, he can open door B or C. If he always opens door B he shifts ...

Once again you are not using the lettering system used by Devlin where the letters are not applied until after the choices are made. Monty does indeed have a choice between two doors but the labels "B" and "C" are not applied until after the contestant choses door "A" and Monty next opens a door. Regardless of which door Monty opens that door is labeled "C" and the remaining door is labeled "B". It is easy to see from this system of labels that the probability that the car is behind door "A" is indeed 1/3 since the contestant has no idea where the car is and that the probability that the car is behind door "C" is zero since Monty never next opens a door with a car behind it. It follows that the probability that the car is behind door "B" is equal to 1 - 1/3 - 0 = 2/3. This agrees with the post by Tattertale where it was explained that the chances of winning are doubled if the contestant switches. However, the contestant would never switch to door "C" because that is the door that Monty opened.

Have a Good Day
KJ Ramsey