Puzzle #1

[Dr. Ivory]

I would change to C. The odds were 2-1 against me getting it right first time. For some reason it has been proven that although the odds are now evens by changing you have a better chance. Saw something like this on Derren Brown.

Cant say I get that. There are three doors. You know nothing about what is behind any door. You pick one at random. One of the doors you didn't choose turns out to have goats behind it, so your chances of having picked the correct door have gone up from one in three to one in two. But you have learnt nothing additional about what is behind either A or C.

Therefore I suggest that as between A and C it is irrelevant that B had goats behind it. But it is also irrelevant that you previously picked A. After B has been opened, the game - effectively - starts again: you have two doors, behind one is the car behind the other is the goat. You have to choose one door at random, you have a fifty/fifty chance of being correct. Therefore choosing either A or C the second time around is equally rational.