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Thread: A unique play in all of blackjack

  1. #1


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    A unique play in all of blackjack

    Gronbog and I were trying to debug a thorny problem that revolved around a rather interesting play. You're playing double deck, S17. In this entire discussion, we're considering only basic strategy; the notion of counting is not involved. You're dealt A,7 vs. the dealer's ace. What's the correct play? You may know that it's to hit. From a fresh deck, this time, you get A,4,3 vs. A. Now what? Well, if you consult the standard, run-of-the-mill BS cards, you will be told to hit your "soft 18" (I loathe the term, but no choice but to use it here). Only that's wrong. If you consult my book or my BS cards, you will see a split box, where the right side shows to hit the two-card holding of A,7 but to stand on the multi-card A,7, or soft 18 (S18), if you must call it by that hideous name.

    Fine. So here's where the plot thickens. Suppose I tell you that you have, forgive me, soft 18, but I don't disclose whether it's the two-card variety of the multi-card holding. NOW what? You tell me that there's really no practical value to this discussion, because you'll always see your hand and you'll always know which it is. But a) trust me when I tell you that this was the source of four days of aggravation between Gronbog and me, trying to debug a problem with our research project, and b) suppose I offered you a million dollars for answering the question correctly. THEN would you care?!

    So, it turns out that the correct answer is to stand. And the reason I titled this post, "A unique play in all of blackjack," is because it is the ONLY play in all of blackjack (any number of decks, any rules), where the multi-card BS play is superior to the two-card BS play. You're probably quite familiar with the other way around, involving 16 vs. T. You probably know that your two-card 16 should always be hit, but that, on average, over all multi-card holdings, standing is better. But, it's also true that when taken as one single play--generic 16 vs. T--hitting is the proper choice; i.e., the multi-card strategy is the WRONG play.

    So, once again, soft 18 vs. A in DD, S17 is the only play in all of blackjack where the multi-card BS (to stand) is superior to the two-card (A,7) strategy to hit, if you don't know which of the two you're holding. And, I suppose, the point is that this information is not so readily available or widespread.

    Don

  2. #2


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    Quote Originally Posted by DSchles View Post
    So, once again, soft 18 vs. A in DD, S17 is the only play in all of blackjack where the multi-card BS (to stand) is superior to the two-card (A,7) strategy to hit, if you don't know which of the two you're holding. And, I suppose, the point is that this information is not so readily available or widespread.
    Don
    So, my stupid question is this : given the above information, does following this this "new" strategy *improve* our overall BS EV? That is, even with this new "violation", we come out on top (or, I should say...we are less deeper in the hole?)

    Also, I wonder if this could be linked somewhat to the post-split BS strategy problem Eric is having as well?

  3. #3


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    Quote Originally Posted by dogman_1234 View Post
    So, my stupid question is this : given the above information, does following this "new" strategy *improve* our overall BS EV? That is, even with this new "violation", we come out on top (or, I should say...we are less deeper in the hole?)

    Also, I wonder if this could be linked somewhat to the post-split BS strategy problem Eric is having as well?
    Yes, sure. Following a composition-dependent BS improves over a strictly total-dependent strategy. The magnitude of the improvement depends on the rules and number of decks. See BJA3, p. 394. It's obvious that the value of using C-D BS is greatest for SD, where it's worth about 0.03%. That drops to about 0.01% for DD, and then it becomes rather negligible for multi-deck.

    Eric's problem is, of course, a great deal more complicated, but there are similarities to the concepts.

    Don

  4. #4


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    Hi Don,

    I ran CA calculation on all possible hand compositions with a soft total of 18, please see results below, it appears that standing is the correct play for multicard soft 18 for the most part. Even for a two cards 1,7 it's pretty damn close!!!

    Soft18.jpg
    Chance favors the prepared mind

  5. #5


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    Quote Originally Posted by iCountNTrack View Post
    Hi Don,

    I ran CA calculation on all possible hand compositions with a soft total of 18, please see results below, it appears that standing is the correct play for multicard soft 18 for the most part. Even for a two cards 1,7 it's pretty damn close!!!Soft18.jpg
    Yes, thanks. And that's the whole point. If you have but a single decision to make all the time, standing is clearly much better. When it's not better, the differences are very small, but when it IS better, the gains can be substantial, often greater than 2% or more. And, although you don't provide the frequencies, there are more instances of the multi-card hands than the two-card A,7s.

    So, the traditional BS cards, which are geared to provide the "right" play for the initial two-card holding, are doing a disservice to the BS player in this particular case.

    Don

  6. #6


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    Don said
    But, it's also true that when taken as one single play--generic 16 vs. T--hitting is the proper choice; i.e., the multi-card strategy is the WRONG play.
    Trivia, not worth much over the course of your lifetime - For the sophisticated counter, a 2 card 16, in a positive count where you have a 6, a bit of a monkey wrench which calls for a hit.

    I believe Flash referred to the margin as a RCH.

  7. #7


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    I believe Flash referred to the margin as a RCH.
    "Pinching pennies" if I remember correctly?

  8. #8


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    Quote Originally Posted by Freightman View Post
    Don said

    Trivia, not worth much over the course of your lifetime - For the sophisticated counter, a 2 card 16, in a positive count where you have a 6, a bit of a monkey wrench which calls for a hit.

    I believe Flash referred to the margin as a RCH.
    Not saying this has any practical importance, especially for us counters, but I believe that the finding is simply not very well known, either by BS players OR counters.

    Don

  9. #9


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    Two questions:

    1. What's wrong with the term "soft 18"?
    2. Are there any DD S17 games still out there?

  10. #10


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    Quote Originally Posted by DSchles View Post
    Not saying this has any practical importance, especially for us counters, but I believe that the finding is simply not very well known, either by BS players OR counters.

    Don
    I would wager that if the question asked of 100 counters not using indexes, 0 would know this. Further, if the same question was asked of 20 competent counters using indexes, only 1 or 2 would answer correctly.

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