When readers ask about table games, they’re often looking not only for “what” and “how,” but also “why.”
So it goes with a couple of recent emails from blackjack players who wanted to drill down to “why.”
One asked, “Why is the house edge lower with one deck than with six? The proportions of the cards are the same no matter how many decks.”
The other was focused on strategy. “Why should I hit soft 18 against a 9, 10 or Ace? Isn’t it an awful risk to break up an 18?”
First things first. Assuming all other rules are equal, fewer decks favor players because more blackjacks are dealt and because you’re more likely to draw a 10-value card in double-down situations.
Other rules often aren’t equal, and six-deck games often have lower house edges than single-deck games. The biggest difference-maker of all is having blackjacks pay only 6-5 instead of the traditional 3-2. That adds 1.4 percent to the house edge and makes any game unplayable regardless of the number of decks.
If other rules are equal, six-deck games have house edges about half a percent higher than one-deck games.
In a single-deck game, if your first card is an Ace, 16 of the other 51 cards are 10 values that will complete your blackjack. That’s 31.37 percent. In a six-decker when you start with an Ace, 96 of 311 cards, or 30.87 percent, are 10s.
Similarly, if you start with a 10 with one deck, 4 of 51 cards, or 7.84 percent, are Aces. With six decks, 24 of 311, or 7.72 percent, are Aces.
Regardless of whether you start with an Ace or a 10, you have a better chance of completing a blackjack with fewer decks.
As for double downs, let’s use 6-5 as an example. With one deck, 16 of 50 cards, 32 percent, are 10s that will give you 21. With six decks, 96 of 310 cards, 30.97 percent, are 10s.
Each card dealt has a greater effect on the composition of the remaining deck when fewer decks are in play.
What about soft 18 vs. 9, 10 or 11? The key is that 18 isn’t as strong a hand as players thing it is. Unless the dealer busts, 18 wins only against 17, pushes 18 and loses to 19, 20 and 21.
Starting with 9 in a six-deck, hit soft 17 game, the dealer will finish with 19, 20 or 21 to beat your 18 on 53.3 percent of hands. It also pushes 18 11.7 percent of the time. You win only 35 percent of hands.
The numbers look similar with 10. The dealer finishes with 19-21 on 52.74 percent of hands and pushes with 18 on 12.10 percent. An Ace up leads to 19-21 on 50.9 percent of hands and 18 on 20.8 percent.
You are an underdog with 18 against those cards and you can’t bust a soft 18 with a one-card hit. So you take your chances on cutting into the dealer edge.
With Ace-7 vs. 9, you cut an average loss of 18.3 cents per dollar wagered when standing to 9.8 with a hit. For Ace-7 vs. 10, average losses are 18.0 cents if you stand and 14.3 if you hit. And for Ace-7 vs. Ace, average losses of 22.5 cents if you stand drop to 16.0 cents if you hit.
You are an underdog with 18 against 9. 10 or Ace, and you can’t bust a soft 18 with a one-card hit. So you take your chances on cutting into the dealer edge.
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