I also think you have googled it too! :P I tried last night lol I found a page with near enough the same answer :P
I still don't full understand it though because
[] < door 1 REVEILD TO SHOW A GOAT
[] < door 2 hidden goat
[] < door 3 hidden car
No matter which of the 2 remaining doors you choose, door 1 has allready been reveild so this door no longer exists in the competition. You're origional door, when all 3 doors were shut, you're chance of getting a car was 1/3. Now that one door has been reveiled to show a goat youre chance of getting a car is 1/2. After the first door is reveild to show a goat it leavs yiou with 2 remaining options of which 1 being a car and 1 being a goat, how possible can you look at it in X/3? :P