I've just used an infinite deck (as it makes for easier probabilities
) and it's actually quite close to 50/50 unless I've made a mistake with my calculations.
I just did the dealer starting with 12 as this was much easier than the soft 17.
The ways that a dealer can bust if on 12 are (brackets are the cards that can produce the 'bust'):-
10
A (9,10) , A,A (8,9,10) , A,A,A (7,8,9,10) , A,A,A,A (6,7,8,9,10)
A,2 (7,8,9,10) , A,A,2 (6,7,8,9,10) , A,2,A (6,7,8,9,10) , A,3 (6,7,8,9,10)
2 (8,9,10) , 2,A (7,8,9,10) , 2,2 (6,7,8,9,10) , 2,A,A (6,7,8,9,10)
3 (7,8,9,10) 3,A (6,7,8,9,10)
4 (6,7,8,9,10)
= (assuming infinite deck) :-
4/13 + 1/13.5/13 + 1/13.1/13.6/13 + ... + 1/13.8/13 (I'm not writing them all out)
If I get time I'll check my calculations but I make the probability of a dealer busting with 12 as 48.6%.
This goes against my initial thoughts as I assumed it would be higher than 50%.
As I said, I'll check through my work but it's getting a little late now.