As the Wikipedia article points out, that problem as stated is ambiguous. You need to know under what circumstances the host would have opened that door. The st

As the Wikipedia article points out, that problem as stated is ambiguous. You need to know under what circumstances the host would have opened that door. The standard assumption is that the host always reveals a door with a goat behind it. However, another possibility is that: (i) if both of the remaining doors contain goats then the host reveals one of them; but (ii) if one of the remaining doors contains the car then the host doesn't open a door at all.