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Thread: If double downing P11 vs D10 is correct, why double downing P10 vs D10 isn't?

  1. #1


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    If double downing P11 vs D10 is correct, why double downing P10 vs D10 isn't?

    The chance of winning (without dealer busting) if you double down P11 vs D10 is ~ 50% (7/13 for you and 7/13 for the dealer). Basic strategy says to double down the P11 vs D10 every time (depending on the rules, I'm talking about S17, NDAS). Does the idea behind this strategy comes because of the dealer busting? Counting the biggest chance to win if the dealer busts getting a 6, hitting 16 (1/2 + 1/13 * 8/13) is ~ 55%. It might be more than 55% including all the possible outcomes but you get the point.

    Not sure if that's correct, and if it's, why given P10 vs D10, doubling down isn't a correct basic strategy move? Winning the double down bet on P10 vs D10 without dealer busting is also ~ 50% and including the highest chance of bust (1/13 * 8/13), also ~ 55%. I'd guess there are few more combinations where the chance is only 50% or even lower but with the bust, the edge goes over to the player. Something has to be wrong with my calculations cause I don't think the basic strategy creators didn't think about it. Maybe adding those outcomes of dealer winning with 3+ cards makes a huge difference.

    I'd guess the end chance if we calculated all the possible outcomes (there are a LOT of them), would be ~ 50% for both. The dealer could win with 3+ cards but I'm not sure if that's enough to take over the edge from the player (he could also hit something below 17 and get a good score as well).

    *P - player
    -D - dealer

  2. #2


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    You are too much fixed on bust rates. The dealer will rarely bust with a 10 upcard. But it should be obvious that P11 is better than P10 because with 11, the player has by default 1 point more than the dealer. The most likely outcome (because Tens are most likely) is that he will win with 21 versus 20, whereas 20 versus 20 is only a push. For a similar reason, you should double down with 10 vs. 9 but not with 10 versus 10, or split (9,9) versus 8 or 9 but not versus 10.

    The dealer bust rate plays a role why you should double down 9 versus 3 through 6, or 8 or (A,8) versus 5 or 6 for single deck or high counts, or soft hands (A,2) - (A,7) versus 2 through 6, depending on your non-ace card, or split (4,4) versus 5 or 6 for DAS.
    Last edited by PinkChip; 11-21-2019 at 07:57 AM.

  3. #3
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    11 vs 10 doubled actually has a win rate of 54% at a neutral count. It is worth it to double unless TC is -3 or worse. 10 vs 10 becomes a Double at TC +5 and no lower.

  4. #4


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    Quote Originally Posted by PinkChip View Post
    But it should be obvious that P11 is better than P10 because with 11, the player has by default 1 point more than the dealer.
    But on 11, getting A will give you 12, while getting a card on 10 will give you 21, so it should level each over and be nor better nor worse, at least what's what I think. When the talking goes about the 50% range, TC is everything. You 100% shouldn't risk it if the TC is unknown to you. If I'm not counting the cards, I usually double down only if the chance of winning is 55-56+% to be sure the negative count won't take over my whole edge. A little risky but it works for me.

    EDIT: Oh yea, sorry Ace won't help us because there's only ~ 1/13 to get it, while getting 10 is ~ 4/13. That's why 11 is better than 10. Thank you

    Quote Originally Posted by LugiaLvl138 View Post
    11 vs 10 doubled actually has a win rate of 54% at a neutral count. It is worth it to double unless TC is -3 or worse. 10 vs 10 becomes a Double at TC +5 and no lower.
    Thank you for clarifying it to me Without counting cards, it's definitely too risky. You're getting those indices from the Illustrious 18 table, right? 10 vs 10 becomes a Double at TC +4 or higher as far as I know and had no idea about the 'It is worth it to double unless TC is -3 or worse' part, there's no such information on the Illustrious 18 table :/

    Indices.1.JPG
    Last edited by LukizKing; 11-21-2019 at 08:17 AM.

  5. #5


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    [QUOTE=LukizKing;279299]If I'm not counting the cards, I usually double down only if the chance of winning is 55-56+% to be sure the negative count won't take over my whole edge. A little risky but it works for me./QUOTE]

    If you don't count, you have no edge. :-)
    Btw. the decision whether to double down depends on two factors:

    1.) Your chance of winning the hand must be greater than 50%
    2.) Your EV of doubling must be greater than the EV of not doubling down (e.g. hitting).

    The second condition is often overlooked or misunderstood.
    Last edited by PinkChip; 11-21-2019 at 10:36 AM.

  6. #6


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    cause if u get a 10, which you will around 30% of the time, u have 21.

  7. #7


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    Quote Originally Posted by PinkChip View Post
    2.) Your EV of doubling must be greater than the EV of not doubling down (e.g. hitting).


    I suppose you just have to follow the full indices and use perfect basic strategy, or there's something I gotta learn, too?

    Sometimes I play just for fun I know I have no edge according to the overall game but it's just somewhat relaxing to play some games without tracking every single card, it got boring to me a little bit.

  8. #8


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    Quote Originally Posted by LukizKing View Post


    I suppose you just have to follow the full indices and use perfect basic strategy, or there's something I gotta learn, too?

    Sometimes I play just for fun I know I have no edge according to the overall game but it's just somewhat relaxing to play some games without tracking every single card, it got boring to me a little bit.
    The EV stuff is already incorporated in the Basic Strategy tables, so you don't need to compute EVs at the tables.
    But regarding your table posted above, to my knowledge, the BS for Single Deck says to double down 8 vs. 5 or 6,
    so the index should not be positive (+3).

  9. #9


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    Quote Originally Posted by PinkChip View Post
    But regarding your table posted above, to my knowledge, the BS for Single Deck says to double down 8 vs. 5 or 6, so the index should not be positive (+3).
    I just checked the basic strategy for single deck games and you're right. I took that table from Google and not using it, so I wasn't aware of that. Thanks

  10. #10
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    I learned from tables as well as YouTube videos and lurking on various sites and forums. 11 vs 10 doubled holds a special place in my heart as my single biggest one hand loss of $200. TC was +3 or so when I made the double and I would do it again without a second of hesitation, albeit at a lower amount until I actually have the bankroll to support $100 mid to max bets

  11. #11


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    Quote Originally Posted by LukizKing View Post
    I just checked the basic strategy for single deck games and you're right. I took that table from Google and not using it, so I wasn't aware of that. Thanks
    I once bought a set of six BS plastic cards (1 deck, 2 deck, 4/6/8 decks, each for S17 and for H17) at Ken Smith's website.
    This summer I also studied some BS charts printed out from Norm's templates, in order to check the differences between
    different rule sets. So it came to my mind that Single Deck demands doubling down 8 vs. 5,6. But I was not sure if this also holds
    for Double Deck, but it does not:

    https://wizardofodds.com/games/black...ategy/2-decks/

    However, these studies helped me in better understanding and memorizing the differences. For instance, the table posted above, containing the index numbers, shows "0 / -2" for Surrender 15 vs. Ace. Since the second index is negative, it says you should surrender this hand also in Basic Strategy. But his holds only for H17, not for S17. Which tells me that posted index table is meant for S17 and H17 (therefore the slash "/"). I remember having seen that you should also surrender 17 vs. A (at least for multiple decks) when H17 in Basic Strategy:

    https://wizardofodds.com/games/black...ategy/4-decks/

    which is not contained in this index table.
    Last edited by PinkChip; 11-21-2019 at 02:45 PM.

  12. #12


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    That's interesting, I guess it's just because they copied it from someone who didn't do a full calculation (I think it takes a lot of time to get those indices, not sure though). In my opinion, it would be a good tip to analyze some of the hands and EV using the hand calculator, at least for me it gives a lot of insights why basic strategy was built the way it is.

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