Ask the Wizard #37
Fred from San Diego, USA
Appendix 1 is based on an infinite deck. Both hands you mention are borderline plays and the number of decks affects which play is better. For example, A-4 against a 4 favors doubling with 26 decks and hitting with 27 decks. A-2 against a 5 also crosses over somewhere between 8 and an infinite number of decks.
Michael from Philadelphia, USA
The Venetian. To the best of my knowledge they are the only casino in Las Vegas which stands on a soft 17 in Spanish 21, lowering the house edge from 0.76% to 0.40%.
Update: The Venetian later switched to hitting a soft 17. As of this update (May 14, 2013) the best Spanish 21 game is at the D, which allows re-doubling.
Danny from Mission Viejo, California
I first addressed this topic in my December 1, 2000, newsletter. For those who missed it I just added blackjack appendix 10 to my site, which explains the effect on the house edge under both a cut card and continuous shuffler game. To answer your question, no, the basic strategy does not change. Basic strategy is always developed based on a freshly shuffled shoe, which is always the case when playing against a continuous shuffler.
Mark from Vancouver, Canada
Let's let d be the number of decks. The probability of a tie on the first round is (4*d-1)/(52*d-1)= 0.073955. The probability of a tie in the second round is 12*4*d/(52*d-2)*(4*d-1)/(52*d-3)+(4*d-2)/(52*d-2)*(4*d-3)/(52*d-3) = 0.073974. Lets call p1 the probability of a tie in the first round and p2 the probability of a tie in the second round. Then the player return is p1*(2*p2 +(1-p2)/2*(1-2))= -0.023301. Multiply by -1 and you have the house edge of 2.33%. I hope I didn't go over this too quickly.